Visual cortex is not just processing what we are seeing trough our eyes, there is also feedback from higher brain regions back to the visual cortex. So when you are dreaming, your visual cortex activates.
Things get more messy though. For example when they take images from cat's visual cortex, they are much clearer because the cat is anesthetized and visual cortex only processes data from eyes. If cat would be awake, it would make reading the image very hard to read.
Sure, I guess I should have mentioned there's some feedback. That's why I said you "probably couldn't"... I don't think we know how much the activated visual cortex corresponds to the imagery we see when we are dreaming.
Things get more messy though. For example when they take images from cat's visual cortex, they are much clearer because the cat is anesthetized and visual cortex only processes data from eyes. If cat would be awake, it would make reading the image very hard to read.
Relevant research with video recording trough much of processing: http://newscenter.berkeley.edu/2011/09/22/brain-movies/