A quick piece of code to create an ascii version of a bitmap from the web, here demo'd with the face of my friend Paul Ford.

asciify.rkt

(require 2htdp/image)

(define ascii-by-density '(#\# #\A #\@ #\% #\$ #\+ #\= #\* #\: #\, #\. #\space))

(define (choose-char cl w h x y)
  (let* ([pixel (list-ref cl (+ x (* y w)))]
         [peak  (max (color-red pixel) (color-green pixel) (color-blue pixel))])
    (if (zero? peak)
        (last ascii-by-density)
        (let ([c (round (- (* (length ascii-by-density) (/ peak 255)) 1))])
          (if (positive? c)
              (list-ref ascii-by-density c)
              (first ascii-by-density))))))

(define (write-asciified-bitmap bm filename)
  (with-output-to-file filename
    (lambda ()
      (let ([w (image-width bm)]
            [h (image-height bm)]
            [cl (image->color-list bm)])
        (for/list ([y (range h)])
          (for/list ([x (range w)])
            (display (choose-char cl w h x y)))
          (display "\n"))))))

;; scaled down to 20% size
(define scaled-ford (scale 0.2 (bitmap/url "http://blog.arc90.com/wp-content/uploads/2013/07/Paul-Ford.jpg")))

(write-asciified-bitmap scaled-ford "ford.txt")