Make a free standing or fridge magnet picture frame for any size picture. You need to add a round magnet to the back to turn it into a fridge magnet. The STL provided is the right size for passport photos, so you can finally turn those horrible extra passport photos you have into fridge magnet gifts for your friends.
This print requires two pieces to fit together, so there's a calibration value to tune the fit for your printer. I recommend you iterate on a small print to find your calibration value. The back changes size with the calibration value, the front remains constant. You may also need to iterate on the perfect fit for your magnet.