Read the requirement carefully
Look for three things: the maximum file size, any exact pixel dimensions, and the accepted formats. Many forms accept JPG only. A kilobyte here means 1024 bytes, so 100 KB is 102,400 bytes.
Step 1: crop first
Empty space costs bytes like everything else. Crop to the subject with the cropper. For a photo with fixed proportions, the passport photo maker crops to a standard size and sets the DPI.
Step 2: set exact dimensions if asked
If the form wants, say, 400 by 500 pixels, use the resizer and turn off the proportion lock.
Step 3: squeeze to the limit
Use the target size tool, which finds the highest quality that fits. If you have a common limit, there are shortcuts for 20 KB, 50 KB, 100 KB, 200 KB and 500 KB. If the form wants a minimum size as well, use the size increaser.
Why uploads still fail
- The file is really a PNG with a .jpg name. Convert it properly instead of renaming it.
- An iPhone photo is HEIC. Convert it to JPG first.
- A transparent PNG turned black when saved as JPG. Pick a white background colour when converting.
- The dimensions are right but the file is too small, and the form has a minimum.
- The photo is huge in pixels, and the form has a pixel limit separate from the size limit.
Check the final file
Look at the result at full size before you submit. Faces and text should still be clear. If they are not, the limit is too tight for that picture, and a plainer background or a closer crop will help more than any setting.