www.homokaasu.org/rasterbator/wizard.gas?Phase=1
Rasterbator allows you to upload any image (jpg, png, bmp, etc.), and turn it into a poster of any size. This web-based tool offers "poster" sizes (from 2'x4' - to quite literally wall-sized - if you've enough ink & paper), and Rasterbator will to the rest.

Your image will be printed, sheet, by sheet, into the poster size you selected. The sheets are printed in ORDER, so that when arranged one after another, left to right, you''ll have a mosaic of your image.

I've tried it small scale (4'x6') and it looks great. Lot's of ink used, lot's of paper as well. All depends on how motivated and creative you are.