Where a 100 KB limit shows up
A 100 KB cap is common on application forms, school admission portals, e-commerce seller dashboards and profile picture fields. It is large enough for a clear passport style photo or a product thumbnail, but far smaller than anything a phone camera produces by default.
If a form says the image must be under 100 KB, aim a little lower, around 95 KB. Some upload systems count a kilobyte as 1,000 bytes and others as 1,024, so a file sitting at exactly the limit can be rejected.
How the automatic target works
Guessing quality by hand is slow. You drag the slider, check the size, drag again. The target mode does that loop for you by testing different quality values and keeping the highest one whose output is still at or under 100 KB.
If a very large photo cannot reach 100 KB by lowering quality alone, the tool also reduces the pixel dimensions. That is the same thing you would do manually, and it is usually the right call, since a 6000 pixel image gains nothing from being kept at full size on a small form field.
PNG files are a special case. PNG is lossless, so quality does not apply to it. To hit the target, a PNG is converted to a lossy format. If you need to keep a PNG, choose a larger target or resize it by percentage instead.
Getting the best look at 100 KB
Crop first. Cutting away empty background means the remaining pixels get more of the file budget. A face photo cropped tightly looks sharper at 100 KB than the same photo with a wide margin of wall.
Photos with smooth areas, such as a plain studio background, compress far better than busy scenes with grass, text or patterns. If a busy image looks rough at 100 KB, try reducing its dimensions to around 1000 pixels on the long side before you compress.
Check the result at full size before uploading. Faces and printed text are where compression damage shows first.
Privacy for documents and ID photos
Photos for forms often include faces, signatures or ID details. Processing happens in your browser, so nothing is sent to us or anyone else. The output also has its EXIF data removed, which includes the location the photo was taken.
A quick workflow that works every time
Open the original from your phone gallery, not a copy that came through a messaging app. Chat apps already recompress pictures, and starting from that copy leaves less to work with.
Add the file, pick the 100 KB preset, and compare the preview with the original at 100 percent zoom. If the face or text looks fine, download it. If it looks rough, crop the picture first and run it again, since a tighter crop means more of the byte budget goes to the part that matters.
Finally, rename the file to something plain such as photo-100kb.jpg. A few upload systems reject names with spaces, brackets or accented letters.