"Moments are temporary, memories are forever"
Look at it this way. A good photographer waits for a moment, a fleeting moment, a moment where everything in the universe seems to fall into place (at least in his/her eyes). He (or she) waits and then he/she sees it, and when he/she does, the moment gets captured in the camera and then us mere mortals can see that moment, which is long gone, again and again. And only then can we see what the hunter saw - the moment (although sometimes I can't even see it after looking at it for a long time). The photographer made the moment into a memory.
But what about the photograph itself. People come by, look at it,appreciate it and at times pretend to appreciate it. But after the crowd has passed, what happens to the picture? It just stays the same. It can do nothing else. And that's what I think happened to Dorian. People admired his beauty for sometime, but after that he had nothing to do. Out of desperation (and possibly boredom) he started to indulge. Was is right? I do not know. He could have possibly used his eternal youth for the greater good. But he was made into a memory of a moment, and the memory of a moment although eternal, the moment itself is still momentary.
P.S. This was not where I was trying to go with this post, but here I am.