I "know" thousands of songs, but like Mmario, there are precious few that I can sing from start to finish without consulting the words or forgetting any. The ones in my performance repertoire rarely have more than 5 verses! But if someone else is singing/leading the song, I can usually sing along. Learining words by heart, even of those I have sung for years, is my problem.
Whereas tunes....different story, no problem, so I reckon I have an audiographic memory, but definitely not a photographic one!