Typical uses for a 100 KB limit
A 100 KB cap is one of the most common upload limits on the web. You will find it on job application portals, university and school admission systems, insurance and benefits claims, tenancy applications, and many internal company tools. It also keeps email attachments light and speeds up uploads on slow mobile connections.
Photos versus documents
Photos are compressed by reducing the JPG quality setting, which smooths away fine texture first. At 100 KB, a photo around 1000 pixels wide still looks good on any screen.
Documents and receipts behave differently: the important information is text, which needs sharp edges. Before compressing, crop the page with the crop tool so no table or floor surrounds it, and photograph it in bright, even light. A clean white background costs very few bytes, leaving more of the budget for crisp text.
How the target is reached
Inside a background Web Worker, the image is decoded and rotated upright. The encoder then tries a quality in the middle of the range, checks the size, and halves the search range repeatedly until it finds the highest quality under 100 KB. This takes six or seven quick encodes. If the minimum acceptable quality is still too large, the image is scaled down by an amount estimated from how far over the target it was, and the search runs again. You always get the largest, sharpest image that fits.
Several files for one application
Applications often ask for a set of uploads: a photo, an ID card, a proof of address and a signature, each under 100 KB. Drop them all in at once. Each file is compressed independently to its own best quality, and the ZIP download gives you the whole set ready to attach.
Units and margins
Upload forms are not consistent about whether a kilobyte is 1,000 or 1,024 bytes. If a form rejects a 99 KB file as too large, set the target to 95 KB in the image compressor to leave a safety margin. Related presets: 50 KB and 200 KB.