I have a suggestion (which I have forwarded to Timothy before, and which was partial inspiration to open this thread) which is as follows:
---sub-folders by alphabet: 0-9, A, B, C, D, E... (first letter of designation - so M1 Abrams would be under "M", PzKpfw.IV under "P" and so on)
---sub-folders by alphabet A, B, C, D, E... (first letter of manufacturers name - so Grumman F-14 would be under "G", Boeing 737 under "B" and so on)
Of course all of it grouped into "Real Life" and "Never Built" sections.
Filenames could contain name of the vehicle plus information about the users depicted on picture, for example drawing of F-14 in the US Navy service could be: Grumman F-14 Tomcat - USA.png - or if there would be more F-14s - Grumman F-14 Tomcat - USA 1/2/3/4...png, alternatively Grumman F-14 Tomcat - USA navy (other options being "air force", "airline", "civil aviation", "army" etc.), blank/generic drawings could in turn contain name only, without "country".
Ships and Spacecraft, due to somewhat limited amount of content could be kept all together.
Sorting these pictures just by alphabet (and general type of vehicle, of course) would allow to avoid problems with drawings containing vehicles of more than one country (with current system they would have to be either posted several times in different folders, posted only in one, but containing content pertaining to other, or edited into several separate files).
Also, currently many folders contain only one sub-folder, with just one sub-sub-folder, often with just one or two drawings inside, so it's lots of clicking of not so much use.