In your opinion, what is the difference between a simple picture, and "photography" as an art? Is it like beauty, just in the eye of the beholder? Or is there a quantifiable aspect to certain pictures that would make them art? I know it's not the subject matter, because even the most mundane and boring objects can be photographed in a beautiful and eye-catching way. And there are plenty of gorgeous things that are not photographed well. So what is it?

I like Jackal's comment about conveying or evoking something. but it takes an eye so compose something that might be pleasing. Somebody has to see the unique or special moments or features of a subject regardless of how ordinary it may seem to most people

Art, for me, has to evoke emotion, certainly. Having "an eye for it" is important, too--and then there is the practiced-skill aspect of deciding what angle to go for, what is in the background, etc.