The file was modified by the source site, for example, by recompressing it to a lower quality. Nothing can be done here.
The source is not where the file originally came from. The uploader got the file from a different source. The source should be changed to point to the original source.
An MD5 hash is a signature used to tell if two files are the same. Two files with the same MD5 hash are exactly the same. Two files with different MD5 hashes are different files, even if they look the same. They may have differences that can't be seen by the naked eye, such as different image compression or quality levels, or different image metadata.
