The Hashing function is a cryptographic algorithm that allows you to “extract” from any digital object (document, photo, video, etc.), an alphanumeric code (fingerprint) that uniquely identifies it.
The Hashing function allows you to extract the fingerprint from a digital object but it is not possible to reconstruct the original digital document from this one.
The Hashing function is deterministic, i.e. it will always generate the same Hash (fingerprint) against the same document source. Every slightest variation of the original digital object, even a simple addition of an empty space, changes its Hash (fingerprint) forever.