I don't think a photo of a dick has ever turned me on, exactly. The context of receiving it might though. I think the hottest picture ever sent to me was from someone I was dating, but hadn't seen naked yet. He put on work boots and a hard hat, and photographed himself in silhouette, the thin light illuminating only the mustard brown of his boots, the Stark white of his slouchy socks, and the caramel of his thick lower legs. I could barely see the faintest hint of his relaxed cock. I always knew he'd look great naked, and the photo showed just enough of his shape that I knew I was correct. THAT photo turned me on. A lot. Like... enough to drive three hours the next day to see for myself.
Some photos here have been arousing, but an important factor generally was the interest I had in the subject as a person.
I do not appreciate unsolicited photos, and I absolutely HATE being told to go look at a gallery. When I do go, it's because the person has been interesting; such people have never had to tell me. An exception would be a heads-up that a gallery I've already complimented has been updated, and the person politely let's me know they have more pictures, just in case I'm interested in looking.