Progressive JPEG would also be cool if bandwidth costs matter, nowadays a lot of images on the web have more pixels than the screen is able to display, so they

Progressive JPEG would also be cool if bandwidth costs matter, nowadays a lot of images on the web have more pixels than the screen is able to display, so they are downloaded and downscaled. Or you have the HTML "imgsrc" attribute for "retina" images. Imagine a file format that says "Byte-ranges 0-n will give you the image for a resolution of 640x480*. Bytes n+1 to m will give you the rest of the pixels for a resolution of 1440x1080, bytes m+1 to the end will give you the pixels you need to add to the 1080p version to get a 2160p version". So the browser would decide what it needs and just requests the file up to that byte... * The low-res 640x480 version might be all the browser needs if the person who designed the web page just wants the image e.g. as a small headline image in a news site column that is 640px wide