I meditated for a long time before writing this post, but at the end of the day I think that - for the sake of automotive history - it's better to share information than to keep for ourselves.
I also believe that it will not damage the spirit of the puzzle game, because when an archive contains several hundred pictures, it's not easier finding anything inside than outside, on the wide web.
So, I propose to start a thread where links and suggestions about big and valuable online automotive archives can be shared.
My first one is the Centro di Documentazione (Documentation Center) of the Turin Auto Museum that - hard to believe - is widely unknown.
Actually, it's not on the Museum homepage and has to be found at
http://95.240.242.254/archidhoc/Login.aspx?CLASSID=552256A (free) registration is needed and it really worths, as it features thousand photos and documents since the eraly age of automotive.