I took a picture off our living room wall that I did not like to make the chalkboard. We've had it for 5 years and bought it at Oops so it wasn't like it was a priceless antique. :)
I painted the frame with a couple coats of white paint we had in our garage.
While the white paint was drying I put a couple coats of chalkboard paint right on the glass. I didn't even mess with taking the picture out.
Once the frame was dry, I sanded the edges a little and put a "glaze" on it. When I say glaze I mean watered down acrylic craft paint. :) I brushed it on with a foam brush and wiped it off with a paper towel until I got the color that I wanted. I let it all dry overnight and then hung it on the wall.