Should a picture thank you card have....

on the front of the card - the bride and groom's names and the wedding date? Or just the words 'thank you'? Or both?

I read once that 'thank you' cards should not have the words 'thank you' preprinted.

so, I'd go with either your names alone, or your names with the wedding date.

Personally, mine only had our first names on them

we had no choice, ours came with Thank You on the front. The pic went inside. (if we did have a choice, it wasn't offered to us) And of course we wrote our own personal thank you on the inside.
I don't think people really notice what it says on the outside.