While the Circle Cutter design from @RabbitEngineering works perfectly, the base of the foot was too wide and that caused that if you wanted to cut a picture that was smaller than the foot base then you could not see the perimeter of the image to beter calculate the center.

This remix includes a the original foot design but with a smaller base diameter

For this cutter I used:

*Cutter 9mm Snap-Off Blade like this one https://www.amazon.com/Cutter-Snap-Off-Blades-50-Blade-BA-50P/dp/B001U73LXU/ref=sr_1_3?ie=UTF8&qid=1520867684&sr=8-3&keywords=cutter+blades (you only need 2 small segments of the blade) *2 screws (I used those you can find in pretty much any computer case for holding the mobo or the PSU) like these http://www.caselabs-store.com/1-4-6-32-silver-hex-head-pc-case-screws-10pk/ *1 small washer, small enough so that the head of the screw does not go through it

Safety note: If the slot where you insert the blade is too narrow, don't even think about pushing the blade with your bare fingers or you might get a nasty cut. Make sure to use gloves and push the blade in using a locking grip wrench or pliers