Its a difficult one PP. I couldn't control it when it happened to me and if it mostly occurs in young children then to identify it, you'd need to be watching for the behaviours that stem from it...like my standing still when it happened...and of course time is ticking if it mostly fades as the child grows up. I suspect if I had been identified and investigated, I would have failed under lab conditions..indeed its only by looking back to my memories of it happening that I can link it with concentration or interest in something. The case that was discussed in my lectures and sorry I can't find any reference, is of a child who could draw silhouette images. Apparently she said she did it by projecting the image onto blank paper and drawing a line around it....but of course that may be how she explained it and not actually what her brain did.
I couldn't zoom in or manipulate the image...could only see what I saw. It used to be said that a "true" eidetiker could be identified by the way their eyes moved when they were "seeing" the image. If asked a question about the image, their eyes would move as though they were looking at a real image, if not, whether faking or mistaken, their eyes would look up and away in the same way that people do when trying to remember something. Does your image recall actually block out what is really there?