Corner Frames from German designer Yvonne Schroeder provides an innovative solution to hanging your pictures in tight spaces. These frames wrap around the corners of your room. The Corner Frame is available in both inside corner and outside corner designs to suit all your nook decorating needs.
The designer’s website is a little short on details but it is available in a few different types of wood and runs about $150-$180 US with the current exchange rate. It’s unclear how the mounting and matte processes work, although I imagine they’re not that different. The only issue I can see with these picture frames is that you will have to bend your photo, so you definitely wouldn’t want to use something rare or irreplaceable.