Unique picture data?

Question

PHP

I want to limit the number of downloads of the same image. That is, one picture can be loaded only once, and the information can be entered into the database. What data is needed for this to be obtained from the image and how best to store it?
Is there anything else besides Exif ? Or will it be enough?

Answer 1

Exif can be removed. I didn't see it in PNG at all. If we are only talking about JPG and do not take into account image scaling - the file size and the last 256 bytes of the file must be quite unique.

Answer 2

calculate and save the same MD5/SHA.
The method is suitable for any file.
however, if at least 1 bit changes in the file, the hash will be different.