Pixels matter more than guessing
Exam forms usually mention width and height in pixels. If the form asks for 200 x 230 pixels, uploading a random square crop may fail even when the file size is correct. First resize to the required dimensions, then compress if the KB limit is still too high.
Keep aspect ratio when possible
If the portal allows a range of dimensions, keep aspect ratio on so the face does not look stretched. If it asks for exact width and height, crop the photo close to the expected shape before resizing.
Common mistakes
Do not paste the photo into a Word document and screenshot it. That often changes clarity and dimensions. Also avoid using a WhatsApp-forwarded image as your source because it may already be compressed badly.
Final check
Before submitting, check three things: image dimensions, file size, and whether the face/signature is clear. If any one fails, the portal may reject the upload.