We have looked into framing many an odd sized image, and more often than not a custom framing job really breaks the bank. Here is a little tutorial on "custom" framing your own images for far less than a professional framer.
What You Need
"odd" sized image
standard frame, larger than your image
paint (if desired)
custom cut mat
acid-free artist's tape
Select and paint your frame. We chose a frame in raw wood (saved a few bucks there) and opted to paint it matte green with acrylic paint. Your frame should be proportionally larger than your image to allow at least a couple of inches around the image. The more mat around your image, the better, in our opinion.
We had a custom mat cut. Instead of a custom frame, which can get expensive, we chose a standard frame size and had the mat cut to fit both our image and the frame. Our mat cost less than $10 to have done. Provided the place you go to uses acid-free mat board and foam core, you needn't go to a high-end frame shop to have this done. Michael's is just fine! Typically, it's really quick and easy, and will save you quite a bit of money.
We opted to hinge our mat board to the backing board using artist's tape to make sure they didn't shift away from one another in the frame, ruining the alignment of the image underneath.
Center your image on your backing board so that it is revealed properly beneath the mat. We use acid-free paper corners to anchor our image and prevent slippage. By taking a strip of paper, folding the ends down to form a point, and trimming it, you get a great corner that can be taped down to the backing board. We didn't have that much border around our image, so we also cut a small triangle out of the top of the corner to create just a small ridge holding the image.
Once the image is placed properly, slide the corners on all corners of the image, being sure not to shift the image. Use acid-free artist's tape to anchor down the corners. You should only have to tape the paper, not the image, preventing any damage to your image. This leaves your image unharmed by adhesive, and you can remove it should you decide later on to frame it differently.
Your image should be centered and secured under the mat at this point, leaving it ready to be assembled. Dust your glass and image, put them back in the frame, and secure! Voila! We framed this oddly sized image for less than $20!
(Images: Jessica Blake Tata)