Brain scans can now retrieve images of what you're looking at. Probably coming soon: images of what you're thinking or dreaming about.
"John-Dylan Haynes of the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany... says it may be possible to 'make a videotape of a dream.'"
That would come too late for me. I haven't had any dreams worth preserving since I finished puberty.