Verifying the certificates issued digitally is a big problem now a days as the digital certificates can be forged easily. You can overcome the difficulties involved in verifying the digital certificates issued by you from your Moodle course by using the Verify Certificate plugin.
This block helps course / site administrators to check / verify certificates based on the code printed on the certificate. It will list all the details for the certificates so it can be manually verified against the copy of the certificate. Read More