General Tips

Memo board
If you are looking for a surface to work on other than a wall or your fridge try the memo board! IKEA makes a nice one that fits the Superhero perfectly. It is called BITS and comes in 2 colors, black or white. Very simple.
Costs about $10.00. Product dimensions Width: 15 3/4 " x Height: 22 7/8 "
(Width: 40 cm x Height: 58 cm)

When you are making your own images use gradations as opposed to just solid color fields. Seen from a distance your eye blends the colors together much better this way.

Color substitution
Substitute colors with grays (or even colors of the same grayscale value). The image will not change all that much, and seen from a distance it looks more photorealistic. Look through your eyelashes for best evaluation of grayscale value.
You can also experiment with replacing pixels in a random fashion. But if you replace too many pixels you will change the image beyond recognition.