... 4 years later I made one of these (but mine is not as cute):
The color of my walls is so close to the color of the burlap that I decided it needed a frame. Suddenly I remembered I had the blind slats that would be perfect.
You will need two slats to make one frame.
Measure the width and length of the frame and subtract 2"
Use a pencil to draw marks on the frame (this will be the inside corners of the frame)
Then draw a 45 degree angle outward from your marks.
Tape slats together using packing tape (you can do several frames at the same time), and make the cuts.
Use glue to adhere the corners together. I was able to borrow some corner clamps to help it dry perfectly.
When the frame was dry, I used a glue gun to put it right on the picture.