It would actually be quite possible to record images from dreams, but we would need imaging technology much better than what we have today. If we could have a resolution high enough to record the activity of each individual neuron in a limited area of the surface of the brain, then recording people's sight, vivid imagination, and dreams would be quite straightforward.
A person's visual field is mapped directly onto an area of the very back of the brain called "V1". Each neuron here is responsible for a specific pixel of the visual field. The map is right on the surface of the brain to a large degree and is easily accessible. Although some parts of it slip down into cracks, these would merely be holes in the field. The area that responds to the main central area that you see with is larger, and can be scanned more easily (In fact that allows the brain to get more information from that area).
Although there are many different maps in the brain that have information about motion, identification, etc., V1 is the primary visual center that has a high-resolution map of what you are seeing. Since there is feedback from other higher regions of the brain, V1 not only responds to the eyes, but to the vivid imagination.
Once a scientist actually did a recording of people's V1 areas and was able to determine things about what the participants were either seeing or vividly imagining. However, since the resolution was very low, he could only tell if the image was large or small, or if it was to the left or right.
Actually, it is possible to record the activity of single neurons by putting electrodes in or near them. So theoritically, it would indeed be very possible to record the visual portion of dreams from V1. However, it would be ridiculously expensive to do this, because it would be necessary to put an an array of electrodes into V1 that would monitor every neuron. It is very difficult to intall even one electrode. A project like this would be kind of like putting an astronaut on Mars or something. Also, the participant would get very bad brain damage, I think, and would probably go blind! Only a mad scientist with enormous resources could do this.
So it actaully is possible to record the visual (and maybe audio and tactile, too) portions of a dream, but it is highly impractical!
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