https://www.electrical-contractor.net/forums/ubbthreads.php/ubb/download/Number/605/filename/DCP_0004.JPG
https://www.electrical-contractor.net/forums/ubbthreads.php/ubb/download/Number/612/filename/DCP_0004.JPG
They may both be the same photo, but they are not the same file.
One file is a file stored with "FILE_ID 605" and the other is a file stored with "FILE_ID 612".
Permissions for each FILE_ID are based on which forum the post lives in, and what the user's access is set to.