How to compress an image to 20KB
Before you add the image, prepare it: crop away everything except the signature or the face, and resize it to the dimensions the form asks for. If the form gives none, a signature around 300–500 pixels wide and a small photo around 400–600 pixels on its longer side are sensible starting points.
Add the image to the box. The target is already set to 20 KB.
Keep the output as JPG unless the form clearly allows another format. Download the result and check that the size reads 20 KB or less.
Zoom in on the file once before you submit it. Every letter of a signature and the features of a face should still be distinct.
Where 20 KB limits appear
Very small limits — 10 KB, 20 KB, 30 KB — usually apply to two kinds of image. The first is a signature: a scan or photo of your handwritten signature, uploaded next to your photo on an application or registration form. The second is a small passport-style photo used on ID cards, admit cards or membership records, where the image is only ever printed or displayed at a few centimetres across.
These limits often come with tight dimensions too, such as a fixed width and height in pixels, and sometimes a minimum size like “at least 10 KB”. Systems use them because they store and print huge numbers of these images. Meeting the limit is easy once the image is the right size; the trouble starts when a full-resolution phone photo is pushed down to 20 KB in one step.
Dimensions matter more than quality
At 20 KB, the number of pixels decides almost everything. Roughly speaking, a small photo can keep about 400–650 pixels on its longer side at a reasonable JPG quality; a 4,000-pixel phone photo cannot fit at any quality without falling apart into blocks. If you add one anyway, the tool reduces its dimensions to make it fit.
So resize first, compress second. Reduce the image to the form’s required dimensions — or to the starting points above — in any photo editor, then compress it here. You will find that the tool can use a much higher quality setting, and the result looks clean instead of smeared.
Signatures are easier than photos. Dark ink on a plain white background is mostly flat color, which JPG stores in very few bytes. A signature image of a few hundred pixels wide often fits well under 20 KB at a good quality.
Tips for signatures and tiny photos
Sign with a dark pen on clean white paper, and photograph or scan it in good, even light; shadows and grey paper add noise that costs bytes and looks dirty after compression. Crop right to the edges of the signature. Increase contrast slightly if the ink looks faint, but avoid heavy sharpening. For photos, use a plain light background and face the light.
If the form asks for a minimum as well, such as 10–20 KB, set a custom target just under the maximum — for example 19 KB — so the file stays inside the range.
On JPG quality: a setting that is too low leaves square blocks and color smudges around edges, which is especially visible on text. If you see that, make the image smaller rather than accepting the blocky result.