'...dreaming is a gradual cognitive achievement that requires the development of visual and spatial skills and other forms of imagistic skills as well.'[1]

Those who've never seen, or who were blinded very early, have auditory dreams. (They dream in sounds.) Those who were blinded after the age of around seven -- when the ability to form mental images necessary for dreaming develops -- are able to dream in pictures.

[1] http://psych.ucsc.edu/dreams/Library/kerr_2004.html