Haven't really thought deeply about this question, but, I think there is very much more to a photograph then just a memory or 'a work of art'. I would personally reserve this term for really great art, like Renaissance paintings, or medieval manuscripts.
I suppose a photograph is a memory for the photographer, but many photos are taken for third parties, to inform (news), as memories (weddings etc), to document (everything under the sun), or to sell (anything, from porn to palaces).
At the moment 'selfies' have become a PR exercise for celebrities, and those who wished they were. And people, broadly, under thirty. Memories, or works of art? Neither, I would say.
A perfect photograph, is a perfect photograph, and we talk about the 'art of photography,' but is it not merely a question of experience, a good eye, creativity,and attention to detail? Is a perfect photograph automatically art? Or just a perfect photograph?
Is a perfectly made dress art?
And can you ever judge art, of any form, totally objectively?
And what is 'Art' in photography? Or even 'Fine Art?' Artistically arranged 'things,' creatively lit and photographed? Digitally manipulated? Absurd things, that no one ever thought of photographing before? ("Ground breaking Art."
You may have opened a can of worms here Chris, as I fear some opinions will clash, and we all know about clashing opinions, in lively debates.