How would you 3D print a stencil? need a design first then model it in Fusion 360 or some other software. then print this in PLA or some other filament. And the print time would be like 3 to 4 hours if your printer is a top of the line. I would just get some pictures in jpg form put it all together in photo shop then take it to the store print out like 3 copies and do like Mick does with his portraits and other art pieces. Much cheaper and faster I would say. If you did not like the design then you just go back to photoshop and change it.