Are partipants registering online?
Because if they are, you can check the credentials they provide as they register against the email a person provides when checking in to the conference.
In your site, include a script that records every email that is successfully registered, and stores that in a db (along with other details like name, ticket number, etc, etc)
At check-in, ask a conference attendee to provide the email they registered with, enter the same in a form, and run a search.
If the email given matches an email in the db, ie matches the email the attendee signed up with, and perhaps other details, then that user is authenticated.
Regards,
Dennis Mithamo.