AVIF is the newest image format in wide use on the web. It is based on the AV1 video codec and usually produces files smaller than both JPG and WebP, which is why more and more sites serve it. Browsers display it without trouble, but outside the browser support is still patchy: older versions of Photoshop and other editors, Windows without the AV1 extension, many print services and a long list of upload forms cannot open an AVIF file. Converting to JPG solves that. This page opens with JPG selected, so you drop the AVIF images and convert; your browser decodes them, so nothing is uploaded. AVIF supports transparency and JPG does not, so transparent areas are filled with the background colour you choose, white by default. If the image needs to keep a transparent background, choose PNG instead in the format buttons. Expect the JPG to be noticeably larger than the AVIF it came from, since AVIF is the more efficient format by some margin. That is the price of compatibility, and quality 85 to 92 keeps the result looking the same. To shrink the JPG afterwards use Image Compressor, and for WebP files from websites see WebP to JPG Converter.
Choosing the right image format for web use has a significant impact on file size and quality. JPEG (Joint Photographic Experts Group) uses lossy compression optimized for photographs: it discards subtle color gradients in ways the human eye does not easily notice, achieving compression ratios of 10:1 to 20:1 at acceptable quality. PNG (Portable Network Graphics) uses lossless compression and supports full transparency (alpha channel), making it ideal for logos, icons, screenshots, and images with sharp edges or text. WebP is Google's modern format that achieves better compression than both JPEG and PNG at equivalent quality: typically 25 to 35 percent smaller than JPEG at the same quality setting, and 26 percent smaller than PNG for lossless images. WebP also supports transparency like PNG. GIF (Graphics Interchange Format) is the oldest format still in use, primarily kept alive by its support for animation. For still images, GIF is inferior to PNG in both quality and compression, limited to 256 colors per frame. Converting to WebP for web delivery is the most impactful single optimization for image-heavy sites. Browser support for WebP is now essentially universal (Chrome, Firefox, Safari 14+, Edge). For cases where legacy Safari support is required, serving WebP via a picture element with a JPEG fallback provides the best result across all browsers.