A hash value is like a fingerprint - just for a file , not a finger . This means that the hash value is a unique string, which is calculated from the file content . As a result, a change to a file has a change in the hash result as well .
I f just the font color will be changed in a text document, the hash value is completely different - even though the content has remained the same . But that is precisely the point of a hash value : to identify an element 100 % .

Applying this to image elements , we can assume, there are almost infinite possibilities to produce a different hash value for one single image element .