JK Brickworks made this amazing “pick and place” style Lego Mosaic Printer:
It is built entirely using LEGO parts. It first uses the EV3 colour sensor to scan the source image and save the data on the Mindstorms unit. It can then print multiple copies from the saved image data. The 1×1 plates used for ‘printing’ the mosaic are supplied using a gravity feed system and the printing head is simply a 1×1 round plate that can pick up and place the 1×1 plates.
More information about this project can be found at JK Brickworks.