Start by measuring the actual requirement
If a form says “up to 100KB”, you need a file below that limit, not merely a smaller-looking photo. A typical 4000-pixel camera photo contains far more detail than most online forms need. Try reducing the width before aggressively lowering JPEG quality.
Resize first when allowed
For a general website image, reducing pixel dimensions often saves more bytes than lowering quality alone. Preserve the source aspect ratio so faces and circles do not become stretched. Use the image resizer if you know the target width.
Adjust compression quality
JPEG and lossy WebP use quality controls. Experiment with a moderate setting such as 75–85 and compare small text, hair, edges and gradients. The optimal result varies by image. The compressor shows actual encoded bytes after processing.
Meeting strict KB limits
If a form requires 50KB or 100KB, use the dedicated 100KB or 50KB target tool. Those tools progressively reduce the resolution if necessary. A strict target may be impossible without unacceptable quality loss.
Keep a backup
Save copies rather than replacing the only full-quality original. Upload the generated output only after checking size, dimensions and readability.