I repurposed an old 20" iMac by using the front bezel with glass panel.
Cut ¼" MDF to size to from a back and glued some sheet metal to it before covering it with black velvet flocking liner..
Then I stuck a strip of white LED lights to the inside of and used magnets to mount a picture.
It all turned out OK. What I did not foresee what how ruthless the LED light would show even the smallest speck of dust on the picture, velvet or inside of the glass. Open to suggestions how to avoid this…