Images in dreams are often generated by expectation. As soon as I think, 'There's a wolf nearby', I'll see a wolf (or perhaps something less terrifying...). But in lucid dreaming I have enjoyed moments when my subconscious surprises me. I've recently been generating ideas for a book cover in my lucid dreams, and it's fascinating to look at a canvas and try to work out why you have been presented with that collection of images? Where do they come from? Are they all memory fragments, or a synthesis? Will we ever know?