Two photos have the same file size, and the resulting comparison matches. Comparisons are made, by default, automatically by selecting a hash method or by performing an exact comparison of files. Registered licence owners have the option to use a SHA1, MD5, MD4, or MD2 hash to compare files. In many cases, using the hashes will be much faster than direct comparisons. With any of the hash algorithms, identified hash duplicates are the same photo for all practical purposes. It is possible, though very very very unlikely, that they could be different.

The last word is that a hash duplicate can and should be considered to be an exact duplicate.