I cut the fabric about an inch wider than the posterboard on all four sides and sprayed the back of it with my favorite spray glue. (My fingers are still sticky - that stuff is serious.)
I laid the posterboard on, smoothed out the creases, and glued down the edges.
I flipped it over, sprayed the back of Lake's picture and stuck it on. Put the frame on it and we were good to go. Another option would have been to cut a hole out of the middle of the posterboard and put the picture behind it like a true mat, but this was easier and had the same effect.
Now on to Lilly's....I looked in my fabric box and found nothing that would go with her room decor. So I started looking around for another option. Wrapping paper! We found one in my stockpile that matched well enough and we went with it.
I actually took a frame that was already on her wall with a butterfly she and I (mostly she) made a long time ago in it. I just reused the butterfly as it was on cardboard to begin with. So I flipped it over and taped the wrapping paper in place.
I put a little spray glue on her picture, stuck it in the middle of the "mat", and put it back in the frame. Done!
You can make mats out of anything and they add so much character. It's such an inexpensive and easy way to spruce up your pictures!
Lilly keeps asking me if I think she looks like Hannah Montana in hers...sure, honey, whatever you say... :)