How to make a digital signature for certificates issued by our project?

Question

Encryption

Hello!
The second day I smoke the documentation on the issue, and decided to ask the experts:
- We have a humanitarian project, in which we want to issue people something like personalized digital certificates. At the same time, we want to protect them from forgery. Digital signature comes to mind. What is the easiest and fastest program to do this? And that there was documentation "for dummies" :) And that it was free.
I was on the site openpgp.org - for some reason there are programs only for mail, but we need something else. We need to somehow sign the picture with the certificate. Well, or at least a Word document. But both are better)) And so that it is simple and does not dislocate the brain.
Thank you!

Answer 1

As an option, insert a QR code with a short (if possible) link into the picture, upon transition to which the same picture will be drawn for verification. The main thing from the link is that it cannot be fabricated, and when the left parameters are slipped, the server issues 404.

Answer 2

The main difference between a self-signed certificate and a certificate from a well-known CA is that users will not need to install your root certificate in the trusted list.
The difficulties are purely technical, but, as practice shows, many people have problems with this.
In general, cryptography and 'for dummies' don't mix well.