Eidetic Memory is a poorly understood concept that may not even exist. If it exists, it’s almost exclusively found in children. Eidetic imagery is not exactly the same as photographic memory, which doesn’t exist.
An article in Scientific American describes eidetic images:
Eidetic images differ from other forms of visual imagery in several important ways. First, an eidetic image is not simply a long afterimage, since afterimages move around when you move your eyes and are usually a different color than the original image. (For example, a flash camera can produce afterimages: the flash is bright white, but the afterimage is a black dot, and the dot moves around every time you move your eyes.) In contrast, a true eidetic image doesnt move as you move your eyes, and it is in the same color as the original picture. Second, a common visual image that we can all create from memory (such as an image of a bedroom) does not have the characteristics of most eidetic images, which almost always fade away involuntarily and part by part. Also, it is not possible to control which parts of an eidetic image fade and which remain visible. Unlike common visual images created from memory, most eidetic images last between about half a minute to several minutes only, and it is possible to voluntarily destroy an eidetic image forever by the simple act of blinking intentionally. Furthermore, once gone from view, rarely can an eidetic image ever be retrieved.
You might expect that an individual who claims to still see a picture after it has been removed would be able to have a perfect memory of the original picture. After all, a perfect memory is what is usually implied by the commonly used phrase “photographic memory.” As it turns out, however, the accuracy of many eidetic images is far from perfect.
Stanford’s Encyclopedia of Philosophy says:
On the other hand, the rare, poorly understood, and controversial phenomenon known as eidetic imagery apparently resembles ordinary mental imagery in intentionality, but is said to be phenomenologically distinct in point of its great vividness, detail, and stability, and because it is “externally projected,” experienced as “out there” rather than “in the head”. Thus the experience of eidetic imagery is supposedly much more akin to seeing a real, external object or scene, than is ordinary imagery experience. (However, eidetikers, as they are sometimes called, are generally reported as having a fair degree of voluntary control over their eidetic images, and rarely if ever seem to mistake them for objective realities.) According to Haber (1979), eidetic ability is found almost exclusively amongst young children, and is fairly rare even amongst them, occurring only in about 2% to 15% of American under-twelves. Furthermore, the eidetic images are said to persist only for a maximum of about four minutes after the visual stimulus of which they are a memory has been removed from sight (Haber & Haber, 1964). Other investigators, however, claim to have found evidence of eidetic ability in adults, particularly ones from “primitive” cultures (Jaensch, 1930; Doob, 1964, 1965, 1966, 1972; Feldman, 1968), and Ahsen (1965, 1977) apparently holds that most or all of us have at least the potential to recall eidetic images virtually at will. (These differences of opinion may, at least partly, arise from different assumptions about the meaning of the ambiguous and contested term “eidetic”.)
It goes on to say:
In fact, there is no scientific consensus regarding the nature, the proper definition, or even the very existence of eidetic imagery, even in children (see the commentaries published with Haber, 1979). Some investigators, most notably Haber (1979), hold that it is a real (albeit elusive), distinct, and sui generis psychological phenomenon, whose mechanisms and psychological functions (if any) may well turn out to be quite different from those of ordinary memory or imagination imagery. Others, however, such as Gray & Gummerman (1975) and Bugelski (1979), argue that reports of eidetic imagery are best understood merely as rather hyperbolic descriptions that are sometimes given, by some children (and, perhaps, the occasional uneducated and illiterate adult), of ordinary (though perhaps particularly vivid) visual memory imagery.
Alan Searleman, professor of psychology at St. Lawrence University, writes:
As it turns out, however, the accuracy of many eidetic images is far from perfect. In fact, besides often being sketchy on some details, it is not unusual for eidetikers to alter visual details and even to invent some that were never in the original. This suggests that eidetic images are certainly not photographic in nature but instead are reconstructed from memory and can be influenced like other memories (both visual and nonvisual) by cognitive biases and expectations. …The vast majority of the people who have been identified as possessing eidetic imagery are children…With a few notable exceptions, however, most research has shown that virtually no adults seem to possess the ability to form eidetic images.
In Enhanced memory ability: Insights from synaesthesia, the authors write:
In the context of memory performance and imagery, it is also important to consider eidetic memory. It can be described as the persistence of a visual image after the according stimulus has been removed (Allport, 1924). It is to be differentiated from non-visual memory and afterimages. In contrast to afterimages, eye movements during stimulus inspection do no prevent eidetic images from occurring, additionally they are positive in colouration and do not shift with eye movements (Girayetal., 1976; Haber, 1979). Eidetic imagery is predominantly, but rarely, found in children from 6 to 12 years and virtually absent in adult populations (Girayetal., 1976). It is important to mention that eidetic imagery is not photographic and hence does not generally benefit memory performance (cf., Haber, 1979).