If you're going to make an assumption, that one is definitely understandable. However, taking a step back, you should have enough representative test cases (QA

If you're going to make an assumption, that one is definitely understandable. However, taking a step back, you should have enough representative test cases (QA snaps a photo with iPhones, tries to upload) that whether assumptions are reasonable doesn't enter into it because you aren't making them.