What is this picture missing?
A corner picture frame!
It's not as hard as you think:
Buy molding from your local chain hardware store, as well as, a midor box kit (which comes with a saw). Cut to your specific size and use wood glue on the corners. The most important part is predrilling nail holes to hang it because the wood will split. Then choose the artsy picture you would like to display and any corner is complete.
I didn't want too much uniformity so I tried to choose a mixture of sizes, painted the frames and mattes, and even added fabric for a little interest.