What fits in 10KB?
Ten kilobytes is very little data, about the size of a short text document. It works well for a scanned signature, which is mostly white paper with a few dark strokes, and for a small head-and-shoulders photo around 200 pixels wide. It also suits icons and thumbnails in lists.
A full phone photo has millions of pixels. To fit in 10 KB it has to give up most of them, so expect a small image. If the upload form lets you choose a larger limit, such as 20 KB or 50 KB, use it and you will get a sharper result.
How to compress a signature or photo to 10KB
Crop away everything you don't need first. Empty margins around a signature still cost bytes. The Signature Resizer and Image Cropper help with this. Then upload the image here. The 10 KB target is already selected.
The output is JPG by default, even when you upload a PNG, so the target applies straight away. You can pick WebP instead, but if you pick PNG the target no longer applies, because PNG is lossless. When the status line says Under 10 KB, download the file.
Getting a cleaner result at 10KB
The compressor lowers quality before it touches the dimensions. For a large photo that can mean a heavily compressed, blocky image that has also been scaled down. You will usually get a cleaner result by resizing first to about 250 to 300 pixels on the long side with the Image Resizer, then compressing the smaller image.
For signatures, a dark pen on clean white paper compresses far better than a grey, shadowy phone photo. Scan or photograph in good light, crop tight, and the file will often land well under the limit without visible artifacts.