Check if your images use modern formats

SiteCurl checks every <img> tag on your page and looks at the file extension. Images using legacy formats (JPEG, PNG, GIF, BMP, TIFF) are flagged. Images using modern formats (WebP, AVIF, SVG) or served through a <picture> element with a modern source pass the check.

The check is smart about edge cases. Data URIs (inline images) are skipped. Images inside a <picture> element that includes a WebP or AVIF source are not flagged, even if the fallback <img> uses JPEG. CDN URLs without file extensions are also skipped since the actual format cannot be determined from the URL alone.

For each flagged image, SiteCurl shows the source URL so you know exactly which files to convert. On a full scan of 50 pages, this covers every visible image across your site.

JPEG was created in 1992. PNG arrived in 1996. Both are still widely used, but they are not efficient by modern standards. WebP, developed by Google, produces files 25-35% smaller than JPEG at equivalent visual quality. AVIF, based on the AV1 video codec, can be 50% smaller. The quality difference is invisible to the human eye in most cases.

The math matters because images are the largest files on most web pages. A typical page loads 1-5 MB of images. If those images were 30% smaller, the page would save 300 KB to 1.5 MB of downloads. On a slow mobile connection at 1 Mbps, that is 2-12 seconds of load time saved.

Browser support for WebP is universal. Every modern browser (Chrome, Firefox, Safari, Edge) supports it as of 2023. AVIF support is newer but covers Chrome, Firefox, and Safari 16.4+. The <picture> element lets you serve AVIF to browsers that support it and fall back to WebP or JPEG for older ones.

Most CDNs and image services (Cloudinary, imgix, Cloudflare Images) can convert images automatically. You upload a JPEG, and the CDN serves WebP or AVIF based on what the browser accepts. No manual conversion needed.

Images are usually the heaviest part of any web page. Switching from JPEG/PNG to WebP can cut total page weight by 20-30% without any visible quality loss. That translates directly to faster load times, lower bandwidth costs, and better scores on Google's speed tests.

Faster pages get more engagement. Studies consistently show that each additional second of load time increases bounce rate by 5-10%. For image-heavy pages (portfolios, product listings, galleries), format optimization has the largest impact of any single speed fix.

Page speed is a confirmed Google ranking factor. Lighthouse specifically checks for modern image formats and flags legacy ones. Fixing this issue directly improves your Lighthouse performance score.

E-commerce sites with product photography benefit the most. A product page with 10 high-quality JPEG images at 200 KB each loads 2 MB of images. Converting to WebP drops that to roughly 1.3 MB. Across a browsing session of 20 product pages, the savings add up to megabytes.

Portfolio and photography sites face a tension between image quality and speed. Modern formats resolve it: AVIF delivers stunning quality at file sizes that load fast even on mobile.

Bloggers who use stock photos or screenshots throughout their posts often have the easiest path to conversion. Most image editors and online tools now export to WebP with one click.

Step 1: Identify legacy images. Run a SiteCurl scan. The image format finding lists how many images use legacy formats and shows example URLs. These are the files that need converting.

Step 2: Convert images to WebP. Use a tool like Squoosh (squoosh.app), ImageMagick, or your image editor's 'Export As' option. Set quality to 80 for photos (visually identical to JPEG at 85). For batch conversion: cwebp -q 80 image.jpg -o image.webp.

Step 3: Use the picture element for fallbacks. Wrap images in a <picture> element to serve WebP with a JPEG fallback: <picture><source srcset="image.webp" type="image/webp"><img src="image.jpg" alt="Description"></picture>. This way, older browsers still see the image.

Step 4: Set up automatic conversion. If you use a CDN like Cloudflare, enable Polish (image optimization) in your dashboard. Services like Cloudinary and imgix convert on the fly based on the browser's Accept header. This eliminates manual conversion entirely.

Step 5: Check your CMS plugins. WordPress has plugins like ShortPixel and Imagify that convert images on upload. Shopify's CDN serves WebP automatically for most image URLs. Check what your platform offers before building a manual workflow.

Converting without checking quality. Always compare the original and converted image side by side. At very low quality settings, WebP can show artifacts around text and edges. Use quality 75-80 for photos and quality 85-90 for images with text.

Serving WebP without a fallback. While WebP browser support is universal in 2026, some email clients and older apps do not support it. Use the <picture> element to provide a JPEG fallback for maximum reach.

Forgetting about images in CSS. Background images set via background-image in CSS are not checked by this scan, but they should also be converted. Use CSS feature queries or multiple backgrounds to serve modern formats in stylesheets.

Re-encoding already compressed images. Converting a heavily compressed JPEG to WebP does not always help. If the JPEG is already at quality 60, converting it to WebP may not save much. Start from the highest quality source you have for the best results.

After converting images, run another SiteCurl scan. The legacy image count should drop to zero. You can also check in your browser dev tools: open the Network tab, reload the page, and filter by 'Img.' The Type column shows the MIME type. Look for image/webp or image/avif instead of image/jpeg or image/png.

Compare total image bytes before and after. The Network tab shows total transfer size at the bottom. A 20-30% reduction in image bytes confirms the conversion is working.

Modern image formats deliver the same visual quality in smaller files. WebP is supported everywhere and saves 25-35% over JPEG. AVIF saves even more. Converting your images is one of the highest-impact speed improvements you can make, and most CDNs can do it automatically.