[drc]

Have him take a photo of the card with a quarter on it or next to it, or otherwise in different setting, to show he physically has the card in hand. Unless he's a photo-shop wizard, this would show it's not a stolen scan.

With the quarter example, he may just assume you want the second photo so you can judge its size. You can tell him you've seen reprints in different sizes, and that's why you want the second photo.

If you know he physically has that card, you should feel safer.