Who asks for 100 KB
The default cap on an enormous number of web forms: school and university portals, visa and licence applications, job boards, older content management systems, and most government e-services. If a form rejected your photo without saying why, 100 KB is the most likely limit it was enforcing.
What fits in 100 KB
Around 1000 × 750 at good quality for a photograph, or a 1200-pixel-wide web image at moderate quality. Comfortably enough for a passport-style photograph to look sharp, and enough for a document scan to stay readable.
What it costs you
Modest for a portrait, more for a landscape. You lose fine texture and some colour gradation, but at normal viewing size most people would not identify the compressed version in a pair. A phone photo of 2–5 MB reaching 100 KB is discarding well over ninety per cent of its bytes, and it holds up better than that sounds.
How this hits the number
Compression quality and file size do not move together in a straight line, so there is no setting that reliably produces 100 KB. This encodes your image repeatedly at different quality levels, narrowing in on the highest one whose output still fits, and returns that file. It never hands back something over the limit, because a file over the limit is the one thing you cannot use.
All of it runs in this browser tab using the canvas API. Your image is read from disk into the page, worked on, and written back out. Nothing is uploaded, which you can confirm yourself — open your browser's network tab and watch it stay empty while the tool runs.
Common questions
How do I make a photo less than 100 KB?
Set the limit to 100 KB and drop the photo in. This searches JPEG quality settings for the highest one whose output still lands under 102,400 bytes, and returns that file. It never hands back a file over the limit, because a file over the limit is the one thing you cannot use.
Will 100 KB be good enough for a passport photo upload?
For an on-screen check, yes — 100 KB is enough for a properly sharp head-and-shoulders photograph. What matters more is meeting the pixel dimensions and background rules the authority specifies, because those are checked far more strictly than file size, and a photo that meets them will fit inside 100 KB without difficulty.
Why is my image still over 100 KB after compressing?
Almost always because the tool you used offered a quality slider rather than a size target, and even its lowest setting was not enough for that many pixels. Reduce the dimensions and the byte target becomes easy to hit. This page works the other way round — you give it the limit, and it finds the quality.