Compress Image to 20KB

20KB is small enough that something has to give, and it is worth knowing what before you upload. A JPEG at this size cannot hold a full-resolution phone photo: a 4000-pixel-wide image has to come down to roughly 300-500 pixels wide before the quality setting alone can carry it the rest of the way. The tool does both, dropping resolution first and quality second, because heavy quality reduction at full size produces the blocky 8x8 artefacts JPEG is famous for while a smaller, cleaner image at the same file size still looks like a photograph.

This size band exists almost entirely because of upload forms. Government portals, exam boards and older enrolment systems often cap a photo at 20KB, a limit set when it was a sensible one and never revisited. If the form also states a required pixel size, check the result against it — some systems reject an image for being too small just as readily as for being too large.

Two things help if the output is softer than you want. Crop tightly before uploading, so every remaining pixel is spent on the subject rather than the background. And if you are compressing a scanned document rather than a photograph, convert it to greyscale first: colour information is a real share of the file, and text loses nothing without it.