Hey there! Here's a Digital Witness that has been shared with you:

Digital Witness

Issued to: WitnusApp user

In witness of the fact that data with the following digital fingerprint existed at the point in time below

Digital Data Fingerprint (Content ID)

01df 51ca 38e9 5728 e6a4 2ed8 e3be d08a 328d 2108 c515 09ee 38a7 2cb0 011a 51fd 95a8 3764 6d5d c1c3 18c8 d3fd e9b9 c252 cde9 fc8d 29f8 9507 7a6e 5746 0502 cdc7

Witness Fingerprint (Witness Id)

011f aefc 0b94 812d b5ed 740c 9bc2 acd7 7fb1 7013 a937 b42a bf15 ea43 5b64 68c6 06f7 12d9 4882 77a1 cc6e 909f cec2 d1a7 5d0a e827 5b9c 42d1 f40d cace 6e12 561a



A Digital Witness proves that something existed at a particular point in time. "Something" can be anything digital, in this case it's this photo taken by a user of the Witnus mobile app:
Evidence image
Here's a short description of the witness, from the person who shared it:
Kongo K4 anlänt på rosteriet
This photo was taken on 9/21/2020 10:45:01 AM (Coordinated Universal Time, UTC)
It was taken here:
If you want to convince yourself that the Digital Witness is legitimate you can validate it yourself, using tools that are freely available on the Internet. Do you want to view the instructions on how to do that?
The app calculates a "fingerprint" of the photo file, and locks this fingerprint in a secure blockchain database to make sure it can't be manipulated. We call this fingerprint the Content Id, because it identifies the content.
A fingerprint is really a very large number, often presented as a long string of letters and numbers. In this case, that string looks like this:
That's pretty unreadable, so we've created an image matrix that represents that string in the form of an image instead. To compare two images, all you need to do is to drag one of them on top of the other. If they are identical, they will match up perfectly. If not, you'll notice because it looks like they are not properly aligned. Give it a try, just push one towards the other!
If the registered fingerprint matches the calculated, as it does here, it means that the content of the photo has not been modified since the time and date the photo was registered. Now let's validate that timestamp!
To do that, we again calculate a fingerprint. This time the fingerprint is based on a string that combines the first fingerprint, a signature that tells us who registered it, and the date and time this happened. Also, at the end of the string we tag on the Id of the user who created it, and the latitude and longitude where the witness was created. The combined string looks like this:
01df51ca38e95728e6a42ed8e3bed08a328d2108c51509ee38a72cb0011a51fd95a837646d5dc1c318c8d3fde9b9c252cde9fc8d29f895077a6e57460502cdc7#2020-09-21T10:45:04.2420330ZWitnusApp userUserIda8913545-1396-4bfc-b3bb-8cd7e6eedbacLatitude57.657318115234375Longitude11.94504299853825
We call the calculated fingerprint of this string the Witness Id, becuase it identifies the Digital Witness. For this particular witness, the Witness Id looks like this:
Again, comparing images is easier (and more fun) than comparing strings of letters, so here you go:
If you want to validate the fingerprints yourself, you can do so by using any service that calculates SHA512 hashes. That's the technical name for the fingerprints, and if you just search for "sha512 online" on the Internet you'll find a number of such tools that are free to use.
To calculate the Content Id fingerprint, you download the media above and upload it to the hashing service and let it do its thing. The result you're looking for is matching fingerprints, that's what tells you that the media file is exactly the one that was registered.
Validating the Witness Id is even easier, you just copy the combined witness string (the one that contains the Content Id, the Signature and the Timestamp, among other things) and paste it into your SHA512 calculator service. It should then print a string that is identical to the Witness Id above. If it does, you know that the timestamp in the witness is identical to the one you just copied and pasted.
The final step is to validate that the Witness Id also has been inserted into a blockchain database, so that you can validate the timestamp of the blockchain transaction. That process is described for this particular Digital Witness on the following page (fair warning, there's quite a bit of math on the page):