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)

3179 cf97 0b2a de29 3a09 8c37 adfd 3c28 0715 ffbc a2cc 8160 ed62 fb4b c134 1850 3a66 a931 314c 0a6a ac05 91ec 0693 db3c 6e23 e165 fb85 8013 76f7 ef69 9a64 5b10

Witness Fingerprint (Witness Id)

1cfe 986e 9bb0 e1ea 5268 0164 82b0 9d2f 411e 191b 8c10 0491 1fcc 6374 a755 6878 26e3 fb84 9eed d31e 9566 8b15 d83a 0199 55c6 244f 6078 30c4 cd1f 2068 ed8f 6de2

Timestamp

2020-09-15T12:00:24.7544960Z

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:
Organic Robusta arrived at the Roastery
This photo was taken on 9/15/2020 12:00:20 PM (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:
3179cf970b2ade293a098c37adfd3c280715ffbca2cc8160ed62fb4bc13418503a66a931314c0a6aac0591ec0693db3c6e23e165fb85801376f7ef699a645b10
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:
3179cf970b2ade293a098c37adfd3c280715ffbca2cc8160ed62fb4bc13418503a66a931314c0a6aac0591ec0693db3c6e23e165fb85801376f7ef699a645b10#2020-09-15T12:00:24.7544960ZWitnusApp userUserIda8913545-1396-4bfc-b3bb-8cd7e6eedbacLatitude57.65728759765625Longitude11.944934859357149
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:
1cfe986e9bb0e1ea5268016482b09d2f411e191b8c1004911fcc6374a755687826e3fb849eedd31e95668b15d83a019955c6244f607830c4cd1f2068ed8f6de2
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):