Images are often the heaviest assets on a webpage, making up 50–80% of a page’s weight. Optimizing them can drastically improve Core Web Vitals – key performance metrics like Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). Poor image practices can slow your site, hurt rankings, and frustrate users. But with the right steps, you can improve performance by 30–50%.
Here’s a quick summary of the 10 tips to optimize images for better Core Web Vitals:
- Use responsive images with
srcsetandsizesto deliver the right size for every device. - Prioritize critical images using
fetchpriority="high". - Preload key images to start downloading them earlier.
- Avoid lazy-loading LCP images to prevent delays.
- Switch to modern formats like WebP and AVIF for smaller file sizes.
- Compress images to reduce file size without losing quality.
- Set explicit width and height attributes to prevent layout shifts.
- Use the
<picture>element for format fallbacks and better compatibility. - Optimize decoding with the
decodingattribute for faster rendering. - Serve images through a CDN for faster delivery and automated optimizations.
These strategies help reduce load times, stabilize layouts, and improve user experience. Start with the basics like preloading your LCP image, switching to WebP/AVIF, and compressing files. The benefits include faster pages, better SEO rankings, and happier users.
Core Web Vitals & Why They Matter – Optimizing Images to Improve Pagespeed & SEO
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1. Use Responsive Images with Srcset and Sizes Attributes
Responsive images solve a big problem: delivering oversized desktop images to mobile devices. This can waste 2–4 times more data than necessary. For example, sending a full desktop hero image (1920×1200px) to a mobile device with a resolution of 360×225px means the image could be up to 28 times larger than needed. Using the srcset and sizes attributes ensures browsers fetch the right image size for each device.
The srcset attribute acts like a menu, offering multiple image versions with width descriptors (e.g., 800w or 1200w). The browser then chooses the best fit based on the user’s screen size. Meanwhile, the sizes attribute tells the browser how much space the image will occupy in your layout – even before CSS fully loads. For example, sizes="(max-width: 600px) 100vw, 800px" means the image will take up the full width of smaller screens but will be limited to 800px on larger ones.
"Responsive images are the primary lever for Largest Contentful Paint (LCP). By serving a 100KB AVIF instead of a 2MB JPEG to a mobile user, you aren’t just saving data; you’re fundamentally improving your search ranking."
– Aqib Iqbal, Lead Developer, SnapResizer
Impact on Core Web Vitals
Optimizing image sizes directly improves LCP by reducing the time it takes to load key resources. Since images are the LCP element on 85% of desktop pages and 76% of mobile pages, using the correct image size is critical. For example, Twitter limited image fidelity to a 2× device pixel ratio, which sped up timeline image loading by 33% without sacrificing noticeable quality.
To avoid layout shifts during loading, always pair srcset with explicit width and height attributes.
Browser Support and Compatibility
The good news? The srcset and sizes attributes are supported by over 97% of modern browsers. For older browsers that don’t recognize these attributes, the image will simply fall back to the src attribute, making this a risk-free upgrade. Additionally, newer features like sizes="auto", which automatically calculates sizes based on CSS layout, are now supported in Chrome 126+ and Edge 126+ as of 2026. With such broad compatibility, implementing responsive images is straightforward.
Ease of Implementation
Start by creating three to five different sizes for each image. This strikes a balance between performance improvements and server storage needs. Use width descriptors (e.g., 800w) for flexible layouts, giving the browser more options. Ensure the sizes attribute aligns with your CSS breakpoints to prevent unnecessary downloads. Tools like sharp, ImageMagick, or frameworks like Next.js‘s Image component can simplify the process of generating responsive image variants.
2. Prioritize Your LCP Image with Fetchpriority
After setting up responsive images, the next step is ensuring your most important image loads as quickly as possible.
Browsers typically assign low priority to images by default, only upgrading them to high priority after calculating the layout and confirming the viewport. This process can cause delays, sometimes referred to as "Resource Load Delay", which is the time between the browser receiving the HTML and starting to download your key image. The fetchpriority="high" attribute addresses this issue by telling the browser upfront that this image is critical and needs to be downloaded immediately.
By adding this attribute to your Largest Contentful Paint (LCP) image, you allow it to download alongside – or even ahead of – scripts and third-party widgets that might otherwise slow things down. In 2023, Google Flights used fetchpriority="high" for its LCP background image and saw its LCP time drop from 2.6 seconds to 1.9 seconds. Similarly, Discord applied this attribute to their LCP image request chain and achieved notable improvements.
Impact on Core Web Vitals
This small adjustment can significantly enhance your Core Web Vitals, which are critical for technical SEO. Data shows that 82% of websites using fetchpriority="high" for their LCP image meet the LCP threshold, compared to just 61% of sites that don’t. On average, pages experience LCP reductions of 100ms to 400ms. Despite these benefits, as of early 2026, only 15–17% of websites take advantage of this attribute, leaving many with slower load times than necessary.
Ease of Implementation
Adding fetchpriority="high" to your LCP image is quick and straightforward. However, it’s important to apply this attribute to only one image – your LCP image – to avoid bandwidth competition among multiple high-priority images. Also, avoid using fetchpriority="high" in combination with loading="lazy". For images that load later, use a <link rel="preload"> in the <head> section to optimize performance. If you’re working with Next.js, simply adding the priority prop to the Image component will automatically handle both fetchpriority and preloading.
Browser Support and Compatibility
As of early 2026, fetchpriority is supported by about 93% of browsers globally, including Chrome (102+), Edge (102+), Firefox (132+), and Safari (17.2+). For older browsers that don’t recognize this attribute, it’s ignored without causing any issues, making this an entirely risk-free optimization. While fetchpriority is considered a hint, modern browsers actively use it to prioritize resources.
3. Preload Critical Images in the Document Head
Preloading critical images is a smart way to ensure they start downloading immediately, building on the benefits of using fetchpriority for your Largest Contentful Paint (LCP) image.
When a browser processes an HTML page, it first needs to identify which images to download. This process introduces delays, especially for images embedded in CSS or loaded via JavaScript. Using the <link rel="preload"> tag helps by telling the browser to begin downloading a specific image right away – even before it finishes parsing the rest of the page.
This approach is particularly effective for CSS background images, which typically load only after the browser processes stylesheets. Web Performance Consultant Arjen Karel puts it best: "Preload the LCP image and the browser starts downloading it before it even finds it in the HTML. Faster download, faster paint. This is one of the easiest wins for the Core Web Vitals".
Impact on Core Web Vitals
The improvement in performance is impressive. Pages that preload their LCP image achieve a "good" Core Web Vitals score 98% of the time, compared to just 88% for pages that don’t use preloading. Moreover, the 75th percentile LCP (p75 LCP) for preloaded images is about twice as fast as for non-preloaded ones. Despite these clear benefits, only 2.1% of mobile pages currently implement preloading – even though 76% of mobile pages rely on an image as their LCP element.
Ease of Implementation
Adding a preload tag is simple. Place <link rel="preload"> in the <head> section of your HTML to kick off early downloads. For responsive images, make sure the imagesrcset and imagesizes attributes match those of the <img> tag to prevent duplicate downloads. Pair preloading with fetchpriority="high" on both the link and the image element, and focus solely on preloading your LCP image to maximize its priority. This technique complements other image optimization strategies, further improving your Core Web Vitals.
Browser Support and Compatibility
Preloading is widely supported, with over 94% of users on modern browsers – like Chrome, Edge, Safari, and Firefox 78+ – able to benefit from it. For older browsers that don’t recognize the tag, there’s no downside – they simply ignore it without any negative impact on performance.
4. Avoid Lazy-Loading Your LCP Image
Lazy loading can help improve page performance when used correctly, but it should never be applied to your LCP (Largest Contentful Paint) image. Surprisingly, around 16% of web pages still make this mistake.
"Never lazy load the LCP image, as this will significantly delay it."
- Arjen Karel, Web Performance Consultant
Here’s why: when an image is lazy-loaded, the browser postpones its download until it predicts the image will enter the viewport. This delay means the LCP image won’t load until after layout calculations are complete. On top of that, lazy-loaded images skip the browser’s preload scanner, which is designed to fetch critical resources early in the loading process. The result? A slower page load and a negative impact on your Core Web Vitals scores.
Impact on Core Web Vitals
Delays caused by lazy loading can significantly affect performance metrics. For instance, web pages using browser-level lazy loading show a median 75th percentile LCP of 3,546 ms, compared to 2,922 ms for pages that load images eagerly. WordPress sites experience a similar trend, with LCP increasing from 3,495 ms (no lazy loading) to 3,768 ms (with lazy loading).
In a July 2021 A/B test on a WordPress site using the "twentytwentyone" theme, disabling lazy loading on archive pages led to 13% faster LCP on desktop (from 2,029 ms to 1,759 ms) and 15% faster LCP on mobile (from 1,657 ms to 1,403 ms). This improvement occurred even though lazy loading reduced image bytes by over 50%.
JavaScript-based lazy loading adds another layer of delay, as the browser cannot preemptively detect custom attributes used for these images.
How to Fix It
The solution is simple: remove the loading="lazy" attribute from your LCP image. Instead, use loading="eager" or leave the attribute out entirely. For even better results, add fetchpriority="high" to signal to the browser that this image is critical.
If you rely on a CMS or optimization plugin, check the documentation for ways to exclude LCP images from lazy loading. Developers can also add a warning system to detect if the LCP image is being lazy-loaded. For example:
new PerformanceObserver((list) => { const latestEntry = list.getEntries().at(-1); if (latestEntry?.element?.getAttribute('loading') === 'lazy') { console.warn('Warning: LCP element was lazy loaded', latestEntry); } }).observe({type: 'largest-contentful-paint', buffered: true}); While lazy loading works well for below-the-fold images, it’s crucial to exclude your LCP image. This approach reduces bandwidth competition and ensures your most important image loads as quickly as possible.
5. Convert Images to Modern Formats (WebP and AVIF)
Modern image formats like WebP and AVIF are game-changers when it comes to reducing load times. Older formats like JPEG and PNG tend to weigh down websites with larger file sizes, but WebP and AVIF deliver similar visual quality at a fraction of the size. Choosing the right format can have a major impact on your search engine optimization and site performance.
For instance, WebP files are 25% to 35% smaller than JPEGs while maintaining the same quality. Even better, AVIF can shrink file sizes by about 50% compared to JPEG and 20–30% compared to WebP. To put it in perspective, a 2 MB hero image in JPEG format might take 3–5 seconds to load. Compressing that same image into a 0.7 MB WebP format can cut load times to under 1.5 seconds.
Impact on Core Web Vitals
Switching to modern formats directly improves Core Web Vitals, particularly Largest Contentful Paint (LCP). Smaller image files mean faster downloads and quicker rendering of key visuals like hero images. Websites using optimized formats have seen up to 47% faster LCP times. These formats also reduce memory usage during image decoding, which helps improve Interaction to Next Paint (INP) by preventing large images from slowing down the main thread. To further optimize, you can use decoding="async" for non-critical images.
Browser Support and Compatibility
The good news? Both WebP and AVIF are widely supported. By 2026, WebP works on 96–98% of global browsers, while AVIF is supported by 94–97%. They’re compatible with modern versions of Chrome, Firefox, Safari, and Edge, though older Apple devices running iOS versions below 16 might not support them.
To ensure compatibility, the <picture> element is the go-to solution. It lets browsers automatically pick the best-supported format. Here’s an example:
<picture> <source srcset="hero.avif" type="image/avif"> <source srcset="hero.webp" type="image/webp"> <img src="hero.jpg" alt="Hero image" width="1200" height="600"> </picture> This setup ensures modern browsers use the most efficient format, while older ones fall back to JPEG.
File Size Reduction Potential
The differences in compression efficiency are striking:
| Format | Avg. Size vs. JPEG | Browser Support | Best Use Case |
|---|---|---|---|
| JPEG | Baseline (100%) | 100% | Legacy fallback |
| WebP | 65–75% | 96–98% | General web images |
| AVIF | 45–65% | 94–97% | High-quality hero images |
For best results, aim for quality settings of 80–85 for WebP and 50–70 for AVIF. This can reduce file sizes by 50–80% without noticeable quality loss. Every extra 100 KB of image data can add roughly 50 ms to LCP on a standard mobile connection, so these optimizations directly translate to faster loading.
If manual conversion sounds daunting, modern CDNs like Cloudinary and Cloudflare Images can handle the heavy lifting. They automatically serve the best format based on the user’s browser. Whether you automate or convert manually, adopting WebP and AVIF should be a standard practice for any performance-focused site in 2026.
6. Compress Images to Reduce File Size
Once you’ve chosen the right image format, the next step is compression. Compression helps shrink file sizes by removing unnecessary data, all while keeping the visual quality intact.
There are two main types of compression: lossy and lossless. Lossy compression works best for photos and large visuals like hero images, cutting file sizes by 50% to 90%. On the other hand, lossless compression is ideal for graphics like logos and icons, achieving a more modest 20% to 30% reduction in size. For JPEG or WebP formats, setting compression levels between 80–85% can reduce file sizes by 60–80% without any noticeable drop in quality. These smaller file sizes not only speed up image loading but also improve essential performance metrics.
Impact on Core Web Vitals
Compression plays a key role in improving Largest Contentful Paint (LCP) by shortening the time it takes to load large image files. Specifically, it reduces the "Resource Load Duration", which should make up less than 40% of the total LCP time. Since images account for the LCP element on 85% of desktop pages, compressing them – even slightly – can have a big impact. For instance, a 2 MB hero image in JPEG format might take 3–5 seconds to load, but compressing it to 0.7 MB as a WebP can cut the load time to under 1.5 seconds.
Compression also affects Interaction to Next Paint (INP) by minimizing delays caused by image decoding on the main thread. To further enhance INP, consider adding the decoding="async" attribute to non-critical images. This ensures that decoding tasks don’t block the main thread, keeping interactions smooth.
File Size Reduction Potential
Real-world examples highlight the benefits of compression. In 2025, an international e-commerce platform used FotoLince to convert catalog images to AVIF/WebP and applied aggressive compression. The result? Their LCP dropped from 4.2 seconds to 1.8 seconds – a 57% improvement. INP also improved significantly, going from 340 ms to 160 ms, a 53% reduction. These technical website transformations led to a 34% increase in mobile conversions and boosted their average SEO ranking by 28 positions. Other websites that optimized images for Core Web Vitals have reported a 23% increase in organic rankings and a 31% drop in mobile bounce rates.
For optimal results, aim to keep file sizes within these practical benchmarks:
- Full-width hero banners: under 200 KB
- Featured images: under 100 KB
- Product thumbnails: under 80 KB
Sticking to these targets ensures faster LCP times and keeps users engaged with your content.
7. Set Explicit Width and Height Attributes
Building on earlier steps like compression and responsive images, explicitly setting width and height attributes for images in your HTML can prevent unexpected layout shifts. By defining these dimensions, the browser calculates the image’s intrinsic aspect ratio and reserves the necessary space before the image loads. Without these attributes, browsers initially allocate no space (0x0 pixels), which leads to content shifting down as images load.
Impact on Core Web Vitals
This approach directly addresses Cumulative Layout Shift (CLS), a metric that tracks unexpected movement of content during page loading. Since images are the Largest Contentful Paint (LCP) element on 85% of desktop pages and often the largest element in the initial viewport on over 70% of webpages, setting explicit dimensions helps stabilize layouts. While this practice doesn’t make images load faster, it ensures smoother visual transitions. For example, one performance test showed that adding explicit dimensions reduced the CLS score by 0.14, effectively eliminating layout shifts for that element.
Ease of Implementation
Adding explicit dimensions is a quick and effective fix. You just need to include the width and height attributes in your <img> tags using the image’s original pixel dimensions. For responsive designs, combine these attributes with CSS rules like max-width: 100%; height: auto; to ensure images remain flexible without distortion. If your site has many images, tools like WP Rocket, LiteSpeed Cache, or EWWW Image Optimizer can automate this process with a single click. To find images missing these attributes, use the "Image elements do not have an explicit width and height" audit in Google Lighthouse or PageSpeed Insights. This simple adjustment complements broader image optimization strategies for improving Core Web Vitals.
Browser Support and Compatibility
The width and height attributes are supported by all browsers. Modern browsers like Chrome (88+), Firefox (89+), and Safari (15+) use these attributes to calculate aspect ratios and prevent layout shifts. The CSS aspect-ratio property, now widely supported, works alongside these HTML attributes to maintain consistent proportions in fluid layouts. However, avoid using CSS rules like width: auto without defined dimensions, as this can result in a 0x0 pixel rendering until the image fully loads.
8. Use the Picture Element for Format Fallbacks
The <picture> element takes the concept of responsive images and format conversion to the next level. By combining multiple <source> elements within a <picture> container, you can serve AVIF to modern browsers, WebP where supported, and fallback formats like JPEG or PNG for older browsers. Browsers evaluate each <source> in sequence, selecting the first compatible format. This approach ensures smaller file sizes and better compatibility, which directly benefits load times and performance metrics like Core Web Vitals.
Impact on Core Web Vitals
Using the <picture> element can have a noticeable effect on your website’s performance. Images account for the Largest Contentful Paint (LCP) element on nearly 70% of web pages, so delivering them in modern formats can significantly improve load times. For instance, AVIF images reduce file sizes by 40–55% compared to JPEG, while WebP achieves a 25–35% reduction. Additionally, specifying width and height attributes on the <img> tag helps reserve layout space, preventing Cumulative Layout Shift (CLS). Smaller image files also free up bandwidth, allowing critical resources, like JavaScript, to load faster. Using decoding="async" further enhances responsiveness.
"Where the srcset attribute gives suggestions to the browser, the
<picture>element directs." – web.dev
Ease of Implementation
Setting up the <picture> element is simple. Arrange <source> elements from the most efficient format (e.g., AVIF) to less efficient ones (e.g., WebP), and include the type attribute (e.g., type="image/avif") to help browsers quickly skip unsupported formats. Always include a fallback <img> tag with a legacy format in the src attribute for older browsers, and ensure this tag has an alt attribute for accessibility. For hero images, adding fetchpriority="high" to the <img> tag ensures they load promptly.
Browser Support and Compatibility
The <picture> element is designed with backward compatibility in mind. If a browser doesn’t recognize <picture>, it will default to rendering the nested <img> tag. As of early 2026, WebP is supported by over 97% of browsers, while AVIF is supported by more than 92%. This means most users will receive optimized images, with older browsers gracefully falling back to JPEG or PNG.
Fallback Format Comparison
| Format | Avg. Size vs. JPEG | Transparency Support | Browser Support |
|---|---|---|---|
| JPEG | Baseline | No | 100% |
| WebP | 25–35% smaller | Yes | 97%+ |
| AVIF | 40–55% smaller | Yes | 92%+ |
9. Optimize Decoding with the Decoding Attribute
The decoding attribute helps you control whether images decode synchronously or asynchronously. This process converts compressed image data into pixels that can be displayed on the screen. To use it, simply include the attribute in your <img> tag.
Impact on Core Web Vitals
When combined with other optimizations, proper use of the decoding attribute can enhance rendering speed. For your Largest Contentful Paint (LCP) image, set decoding="sync" to ensure it decodes immediately. For other images, especially those below the fold, use decoding="async". This shifts decoding tasks away from the main thread, keeping your page responsive and avoiding browser freezes during heavy decoding. This is especially important since images contribute to the LCP metric on 85% of desktop pages and 76% of mobile pages.
"By adding
decoding="async"to your images, you move the resource-intensive decoding off the main thread. This allows the UI to stay responsive even while heavy visual assets are being processed into memory."
- Aqib Iqbal, Lead Developer, SnapResizer
These settings align smoothly with modern browser capabilities, making them a practical addition to your optimization toolkit.
Ease of Implementation
For your LCP image, pair decoding="sync" with loading="eager" to ensure it renders as quickly as possible. For other images, especially those below the fold, use decoding="async" alongside loading="lazy" to improve performance. Keep in mind that the decoding attribute cannot be applied to CSS background images, so avoid using them for critical assets.
| Image Type | Recommended Decoding | Impacted Metric |
|---|---|---|
| LCP / Hero Image | sync |
LCP |
| Above-the-fold (Secondary) | async |
INP |
| Below-the-fold | async |
INP |
Using optimized decoding works hand in hand with other strategies to improve your Core Web Vitals metrics.
Browser Support and Compatibility
As of 2026, the decoding attribute is supported by all modern browsers. For browsers that don’t recognize it, the attribute is simply ignored, and the default behavior is applied without causing any issues.
10. Serve Images Through a CDN
Serving images through a Content Delivery Network (CDN) takes your website’s performance up a notch by speeding up image delivery. A CDN works by caching your images at edge locations worldwide, ensuring users receive content from the server closest to them. For example, someone in Tokyo will get images from a Tokyo-based server, while a user in New York will get content from a New York server. This reduces the distance data has to travel, cutting down load times and boosting Core Web Vitals scores.
Impact on Core Web Vitals
Using a CDN significantly improves your Largest Contentful Paint (LCP) by reducing both Time to First Byte (TTFB) and resource load duration. In fact, implementing a global CDN can slash image delivery latency by 40–60%. Many modern CDNs also automatically convert images into next-gen formats like WebP or AVIF, which reduces file sizes by 40–80%.
For example, in October 2025, the Weekerp Blog adopted the Weekerp Image CDN to enhance their technical SEO. By transitioning from serving raw PNG files on a Next.js server to using the CDN with automated WebP conversion and edge caching, they achieved dramatic results. Image load times dropped from 36ms to just 3ms – a 10x improvement – and the average image file size shrank from 30.2KB to 3KB, representing a 20x reduction in payload.
"A CDN shortens the physical distance between your server and the user, improving response time and transfer speed. With cached assets at edge locations, your content loads faster anywhere in the world."
- M.J. Kang, Growth Specialist, Weekerp
Smaller, compressed files also reduce browser download and decoding times, freeing up the main thread and improving Interaction to Next Paint (INP) scores.
Ease of Implementation
Modern CDNs make implementation straightforward with URL-based transformations. You can adjust image size, quality, and format directly within the image URL using parameters like quality=auto or f_auto. Enabling automatic settings (e.g., f_auto,q_auto) allows the CDN to pick the best format based on the user’s browser and network conditions. Additionally, setting up origin pull ensures automated caching, and configuring a cache TTL of at least 30 days helps maintain efficiency.
To keep things organized and future-proof, use a custom subdomain (like images.example.com) for your CDN endpoints. This approach not only reinforces your branding but also makes it easier to switch providers later without updating URLs. An effective CDN setup should aim for a Cache Hit Ratio above 95%.
| Feature | Standard Web Server | Image CDN |
|---|---|---|
| TTFB | High (depends on distance) | Low (served from nearest edge) |
| Format Conversion | Manual/Build-time | Automatic/On-the-fly |
| Resizing | Pre-generated sets | Dynamic via URL parameters |
| Compression | Static | Context-aware (device/browser) |
Browser Support and Compatibility
Modern CDNs use the Accept request header to detect browser capabilities seamlessly. This ensures that formats like AVIF are served to browsers like Chrome and Safari, while older browsers receive WebP or JPEG fallbacks – all handled automatically. No extra configuration is needed on your part, as the CDN takes care of these optimizations behind the scenes.
Image Format Comparison Table
Image Format Comparison: JPEG vs WebP vs AVIF for Core Web Vitals
Here’s a handy table to help you pick the right image format for your specific needs. Choosing the correct format can improve both Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS).
| Feature | JPEG | WebP | AVIF |
|---|---|---|---|
| Relative File Size | 100% (Baseline) | 65–75% (25–35% smaller) | 45–55% (50%+ smaller) |
| Global Browser Support | ~100% | 96–99% | 94–97% |
| Transparency | No | Yes | Yes |
| HDR Support | No (8-bit only) | No (8-bit only) | Yes (10/12-bit) |
| Animation | No | Yes | Yes |
| Best Use Case | Legacy fallback, Email | General UI, Thumbnails | Hero images, High-quality photos |
Key Takeaways
JPEG is now mostly used as a fallback for older browsers and email clients. It’s reliable but lacks modern features like transparency and HDR support.
WebP has become the go-to format for most web graphics. With near-universal browser support (96–99%), it offers excellent compression, supports transparency, and decodes faster than AVIF. This makes it perfect for UI elements and thumbnails.
AVIF stands out for its unmatched compression – files are 50% smaller than JPEG and 20–30% smaller than WebP. It’s especially suited for high-quality visuals, like hero images, thanks to its HDR support (10-bit and 12-bit color depth). For instance, at the 90th percentile of web images, AVIF files average just 45 KB compared to 274 KB for JPEG.
"AVIF is the undisputed compression king of 2026."
- SnapResizer
Best Practices for Implementation
For the best performance, use a progressive fallback strategy:
- Serve AVIF to modern browsers for its superior compression and HDR capabilities.
- Use WebP as a fallback for browsers that don’t support AVIF.
- Keep JPEG as the final fallback for legacy systems, especially in email clients.
Conclusion
Optimizing images isn’t just another item on your to-do list – it’s the most impactful step you can take to improve your Core Web Vitals. With images making up 50–80% of a typical page’s weight and driving the Largest Contentful Paint (LCP) on 85% of desktop pages, addressing image performance issues yields immediate, measurable improvements.
The results speak for themselves. Sites that adopted these strategies experienced Core Web Vitals improvements of 25–40%, leading to better search rankings, reduced bounce rates, and higher conversion rates. For instance, one global e-commerce site slashed their LCP from 4.2 seconds to 1.8 seconds – a 57% improvement – and saw a 34% boost in mobile conversions alongside an average SEO ranking jump of 28 positions.
Start with the essentials: preload your LCP image, define explicit dimensions, and switch to modern formats like WebP or AVIF. These three steps alone can tackle the most common performance bottlenecks. Here’s a compelling stat: 83% of pages with a preloaded LCP image achieve a "good" LCP score, compared to just 65% of pages without preloading.
The best part? Many of these improvements can be automated using your CDN or build tools, saving you the hassle of manually optimizing every image. Begin by perfecting your hero images – they have the biggest impact – and then work your way through the rest of your page.
The payoff is instant. Faster load times, stable layouts, and smooth interactions create an experience your visitors will love – and Google will reward.
FAQs
How do I find my LCP image?
To pinpoint your Largest Contentful Paint (LCP) image, focus on the largest visible element on your page. This could be a hero image, background image, or even a video thumbnail. Tools like Google Search Console or Chrome DevTools are incredibly helpful. In Chrome DevTools, head to the Performance tab, record a page load, and locate the LCP marker. This marker will pinpoint the element contributing to your LCP.
Should I use preload or fetchpriority?
For better image optimization and faster Core Web Vitals performance, consider using fetchpriority="high" or preload on critical images, especially the Largest Contentful Paint (LCP) image. These techniques help reduce LCP and improve overall load times.
preloadensures that critical resources are loaded early by instructing the browser to prioritize them.fetchprioritygives the browser clear instructions about the importance of specific resources, leading to quicker rendering.
For optimal results, use both methods together on critical images that directly affect LCP. This combination ensures faster loading and a smoother user experience.
What image format should I use for each page?
When it comes to optimizing images for Core Web Vitals, the top choices are WebP and AVIF.
- WebP: This format is widely supported by browsers (with over 97% coverage expected by 2026) and offers excellent compression for smaller file sizes without sacrificing quality.
- AVIF: Known for even better compression than WebP, AVIF also supports advanced features like HDR and a wide color gamut, making it ideal for high-quality visuals.
For best results, use WebP for broad compatibility, AVIF for cutting-edge features when supported, JPEG as a fallback option, and PNG when you need transparency in graphics.
