10 KB is the tightest limit you'll usually meet, and it is almost always for signatures or thumb impressions. A clean signature on white paper, trimmed to the ink and saved at the required pixels (often around 140 × 60), fits under 10 KB easily — the hard part tends to be forms that also set a minimum, so check both numbers. For a photo, 10 KB only works at small dimensions; if your photo can't get there, reduce the pixel size first. Switch the editor to Signature mode for automatic paper cleanup.
New to KB limits? Read the full guide on the compress to 50 KB page: how the compression works, 1,000 vs 1,024 bytes, min–max ranges and keeping photos sharp.