The point about looking terrible in photos is that we think we look terrible, but others do not.
This was brought home to me recently when I looked through old photos. I have never looked good in photos, if you ask me, so imagine my surprise looking at a photo of myself aged twenty-five, when I caught myself thinking who is that attractive, pretty young woman? Followed by Help, it's me!
So, go to the wedding, stand where your son and daughter-in-law want you to when photos are being taken, and look happy.
If they give you a copy of the photo of the whole family, you don't need to display it, and indeed they will feel complimented if you ask if you can have one of the bride and bridegroom alone.