Ancient showed some framed pics on the walls of Stormwind - I have never personally looked at the pictures there as I'm too busy running for my life looking for somewhere to hide! But maybe it's just Stormwind that has a bit of an art paucity. There are many fine examples of art scattered throughout Azeroth. And of course there are some which are not so fine.
These were on the wall of a house in Tanaris. I don't quite remember what it was but there were Southsea pirates or some sort there, so I assume it was a quest. Looks like it was a family home before the pirates came. Wonder who all these people are?
Goblins have an interesting idea about art. At least they have their resort rooms decorated with pictures.
And here is the selection of Dalaran art. As limited as Stormwind, I have to say. Lots of pictures of Northrend scenery! I have to say that "big fish catch" is a bit... gruesome.
So what other works of arts have you seen around Azeroth? If I find any more I'll have to update this post.