100 KB is a typical limit for scanned certificates, ID cards, mark sheets and larger photos on application and KYC portals. This tool produces a JPG of at most 100,000 bytes from your photo or scan. It tries JPG quality from 95% down to 50% and keeps the highest one that fits, so text in scans stays as readable as the limit allows.
At 100 KB most phone photos only need a lower quality and a moderate size reduction, so results usually keep plenty of detail. If quality alone isn't enough, the image is scaled down until it fits, and the result shows the final pixel size and quality. You can also force an exact pixel size when a portal specifies one.
The output is always JPG, the format almost every portal accepts. A KB is counted as 1,000 bytes so the file passes either way of counting. Multi-page documents and PDFs aren't handled here: this tool takes images, one file in and one JPG out per image.