Digital fingerprint
Two identical files give the same fingerprint; changing a single byte changes it completely. This is the calculation on which all digital proof rests, and it happens here, in your browser.
Two files, two photos, two recordings, two videos, two texts: drop one on each side. Both fingerprints are calculated in your browser, and only the fingerprints are compared. The items themselves never leave your device.
Paste the fingerprint you were given here. Case and spaces do not matter.
How it works
The SHA-256 calculation turns any content into a short string of characters: its fingerprint. The same content always gives the same fingerprint; the slightest change produces a completely different one.
A photo, a contract, a video: any content, of any size.
Short, unique, always the same for this file.
7d3a 91c4 5be0 …A single byte changes: a pixel, a comma, a date.
The change is obvious: nothing to guess, nothing to interpret.
f082 4e77 a1c9 …The fingerprint cannot be used to reconstruct the content: it identifies the content without revealing it. This is what makes it possible to prove a document's integrity without ever disclosing it.
What a fingerprint does not prove
A fingerprint attests that a file has not changed since the fingerprint was calculated. It says nothing about what happened before. If the photo was edited before you hashed it, the fingerprint seals the edited version.
That is why the Scealia app calculates the fingerprint and timestamps it at the moment of capture, on the device, before the file could have been modified.