I have worked out the processing sketch. i will threshold the image so its only black and white and the get an array of values which correspond to the pixel colour. I will pass this array as a string to the arduino and "print" out the picture in an array format from to to bottom or whatever way you like. I was thinking of doing it with a 2d array controlled with stepper motors either moving the brush/pen or moving the canvas. but i thought it would be more interesting using 2 pulleys above the canvas held vertically and suspend the pen/brush/ink from the pulleys.
you think this will work?