A scan of the certificate would be what I'd expect, if I asked for it.
You'd possibly want to bring the certificates to the interview, if this is relevant to your situation. Generally this is more for HRs benefit than the interviewers' - by which I mean, these policies/processes are typically driven by HR rules (which themselves are designed to catch rare/ridiculous 'worst case' scenarios) rather than a burning passion from the professor doing the interview to see a candidate's life history in print, signed in triplicate!
In short - send a quick scan; if they're not happy with it they'll let you know what they do want, and either way it shouldn't affect your chances.