Quick answer
The safest assumption is that the portal wants a JPG with a strict file size and sensible image dimensions. That is why a size target plus optional resizing works well for these forms.
If the website says the image must be under 50KB or 100KB, start there. If it also rejects the file after compression, reduce the width and height slightly. This usually fixes the most common combination of size and dimension errors.
What usually works best
Another frequent issue is using PNG when the portal expects JPG or JPEG. PNG is fine for many uses, but passport and identity systems often behave better with JPG because it is a more common upload format for photo-based forms.
People often lose time because they solve only one part of the problem. They compress the file size but forget the dimensions. Or they resize the image but forget the format. ExactSizer helps because it covers those final adjustments in one place.
If it still fails
The same approach also helps with school registrations, national ID services, exam portals, and public administration sites that use the same kind of old upload logic and vague rejection messages.