I just thought I'd post a couple of links to sites that give examples of ekphrastic poetry as well as detailed explanations. In short, if I haven't already said this elsewhere (which I may have), ekphrastic poetry is poetry that responds to, evokes, or is informed in some way by another work of art. It doesn't just describe the artwork, it explores it; illuminates it.
I'm hip-deep in the process of selecting work for the ekphrastic issue. Lot's of good stuff, I'm afraid. It's going to make it tough to choose.
Anyway, here are links. Happy reading.
Some examples, including classic works like Keats' "Ode on Grecian Urn"
Examples and explanation by Jennifer Bosveld of Puddinghouse Press