Many websites will serve you a WebP file instead of JPEG/PNG if you say that you can handle WebP. While WebP is generally an acceptable format for serving web content, it’s an annoying format for images that you actually want to save to disk/archive - see my comment here as to why. Even if WebP was a fine format, odds are you’re downloading a 2nd-generation lossy image converted from a JPEG/PNG, so it’s usually better to just get the source file instead.