There is a story that old Immanuel Kant was incapable of calling images to mind. Similarly, I think in terms of words, concepts, formal propositions, and syllogisms, which manifest in abstruse networks of ideas and subtile chains of reasoning.
This helps explain why the abstract thinker can expound on Tolstoy's War and Peace in great detail, yet can't always decide where precisely he parked. Personally, I remember what I think easier than what I've seen. If I've thought about what I've seen, then I remember what I've seen only because I've thought about it. But thoughts are stored as pieces of text rather than photos. One might ask: why are some memories preserved while others are are not? Furthermore, what format is most economical?
I submit that memory is a principle of selection. It should prove impossible for any human to remember everything they've ever seen, heard, thought about, and so on. Even walking through a parking lot on a given day one sees various licence plate numbers, absorbs lots of scenary, hears many conversations, and so forth. Yet, just because one looks at something does not mean they've seen it, and just because they've seen it does not necessarily mean they've registered it as a conscious thought (the detail could be preserved in the unconscious mind). This could be the case when a particular licence plate number from a parking lot of thousands of cars presents itself as a detail in one's dream, yet nowhere was such a thought registered conscously. Finally, even if a thought makes it to the lofty heights of consciousness, this does not gaurantee that it will be accessible in its original form at a future date. Yet, humans naturally tend to remember things that affect them personally and conduce to, or get in the way of, their desires.
Now, why might it be more advantageous to store information as an encyclopedia rather than a picture book? An observation about computers can help us decide which is more economical. An arbitrary picture (1024x768 in JPEG) takes up roughly 166,244 bytes, while a 1000 word essay in PDF format is about 20,500 bytes. Now, if people are not being thoughtless when they say a picture is worth a thousand words, (and the strict thinker must hold one to the letter, as the spirit is inevitably inconsistent), it is clear by virtue of how much space it requires to store each that the computer can have eight thousand-page essays for every one picture. Thus, either people are wrong, which they often are, and a picture is worth more than a thousand words, or people are right and we are lead into the following. Given that rational choice holds that the rational decision-maker must opt for the most utility-maximizing option among the competing alternatives, textbook thinking clearly gives one a better bang for their buck, and is therefore a more productive area for the allocation of intellectual resources. Though, I admit there are likely exceptions where the value of storing a picture outweighs the value of storing text depending on one's point of view. From the point of view of a family man, he wants to have an image of what his wife and children look like. He will inevitably give up the eight essays for a clear picture of his wife for his mind's eye to look at so long as there's still books in the library. But supposing his wife died, all pictures of her were lost, and all he was left with is his textbook-like stories about her (though unable to call her image to his mind) would he be willing to give up all his stories in exchange for only one picture? I'd keep the text. What would you do?