Photographic memory is one of those concepts that is understood and shown by pop-psychology and the media a lot more than it is shown by academic psychology- just think of how many films, books and TVshows you’ve seen featuring a character with a perfect or almost perfect memory for everything.
However, in real life, photographic memory cannot be easily found, and scientists and psychology are still debating whether it actually exists. People have often come forward saying they have an exceptional or photographic memory, but often they are found to be mistaken, and there are only a few cases of people that could genuinely have a photographic memory.
Based on what I know about memory (and with a little help from Wikipedia) there are four things that can lead to having a better memory than average. For each of these, I have mini-theories of whether these could turn into photographic memory if it exists, and how they might work. The first one is here, and the others will be up in a few days.
Hyperthymesia is a condition where people have enhanced autobiographical memories, and enhanced episodic memory associated with that. In non-psychologist terms, that means they have an amazing memory for exact events in their own life, and for outside information that happened around those events. People with hyperthymesia remember what happened on every day of their life from a certain point, as well as the weather, temperature, and even what people were wearing on that day.
So at first glance, this seems like it could lead to photographic memory, as people with hyperthymesia could simply associate images, facts, conversations etc with the exact day they learned them, keeping them in their store of memory.
However, there are problems with this theory, and with the condition itself. So far, scientists believe they have found 20 people with hyperthymesia, while 6 have been confirmed, which is nowhere near the amount of people who claim to have photographic memory. Also, many of the people found to have such an amazing memory of their own life also deliberately study and memorise their lives, through keeping highly detailed diaries and regularly re-reading them. That’s not to say their memory is entirely due to their rehearsal, just that experiments should be done into whether people with no such extensive journaling and rehearsal can have the same ability.
Also, brain scans of the most famous hyperthymesic, Jill Price, show some neurological differences in her brain (some of which are associated with autism, though she is not autistic). One proposed theory for her memory is that she lacks control over a part of the brain that stops conscious recollection- by this logic, she remembers all her personal experiences, as her brain does not know what information it can safely ignore.