[chainsoar]

They probably dream colours, shapes, and all sorts of things that the mind of a seeing person, having been raised with some order in the world in terms of sight, could not comprehend. Their minds may well try to formulate pictures of what it thinks things might look like. It may try to piece together pictures of things the person is familiar with by touch. I'm sure blind people wonder at least sometimes what a person looks like, even if they know them by feeling the contours of their face and so on. But either way, I wouldn't say it was impossible for them to dream pictures, since dreams have nothing to do with the optic nerve that they lack.