Mostly through Google Image Search, but I also look at Hunk O’Pedia (updated) and It’s not porn, it’s Art (sadly not updated; the last post was in December 2015).
Personally, I still find Google Images to be the best of them because while those blogs I mentioned offer a lot of photos, it can be tough to find a photo that has a specific theme in it. 🙂
Grazie!
~ Signora Paola