For your scanned images at least, sequence numbers are probably a very good solution. Unless there are other things that make your files unique, make sure you allow for enough digits in the number though as otherwise you might end up with duplicates. That also goes for the frame number; that is only 4 digits so after only 10.000 images you're back to the first. So perhaps to be on the safe side and allow for 5 or, better yet, 6 digits.
Does this answer your question?