Much of the current popular controversy surrounding eidetic memory results from an over application of the term to almost any example of extraordinary memory skill. The existence of extraordinary memory skills is reasonably well-documented, and appears to result from a combination of innate skills, learned tactics, and extraordinary knowledge bases (you can remember more of what you understand than you can of meaningless or unconnected information.) Technically, though, eidetic memory means memory for a sensory event that is as accurate as if the person were still viewing, or hearing, the original object or event. Almost all claims of "eidetic memory" fall well outside this narrow definition. A handful of recent studies have suggested that there may be a few, rare individuals who are capable of a limited amount of eidetic recall. This recall is theorized to be essentially 'unprocessed' sensory memory of raw sensory events. (i.e. "raw" images devoid of the additional (usually automatic) perceptual processing, which in normal memory inseparably attaches to the image information about the object's identity and meaning. The documented eidetic abilities, however, appear to be far more circumscribed, and far less common than popularly imagined.
Marvin Minsky, in his book The Society of Mind, was unable to verify claims of eidetic memory and considered reports of eidetic memory to be an "unfounded myth".An example of extraordinary memory abilities being ascribed to eidetic memory comes from the popular interpretations of Adriaan de Groot's classic experiments into the ability of chess Grandmasters to memorize complex positions of chess pieces on a chess board. Initially it was found that these experts could recall surprising amounts of information, far more than non-experts, suggesting eidetic skills. However, when the experts were presented with arrangements of chess pieces that could never occur in a game, their recall was no better than the non-experts, implying that they had developed an ability to organize certain types of information, rather than possessing innate eidetic ability.
This seems like as good an opportunity as any to clear up the greatest enduring myth about human memory. Lots of people claim to have a photographic memory, but nobody actually does. Nobody.