I have had a yahoo account for as long as I can remember, but i don't use it now. But I log into it once every 2 months after I get a complaint of a friend saying "check your email". I check my Gmail accounts everyday, They just sent it to the wrong addresss. I have told them noumerous times, I have been using my Gmail account a few months after they opened up the service.
Error404, They are bound to check the headers of the files and see that they are images. I have never really read the ToS specifically for Gmail, But there is bound to be "periodic checking of legitimate use".
I never really made it habit to store files in my email. I find it slow and tedious. If I have to send files, I usually put it in a passworded Rar/ZIP. That way, its all encrypted and they can't see what file names are inside. In fact I might have one or two files in my gmail that are pirated... Just gotta guess the password.
Also, Error404 similar to Software stored at my school. The files and serials were all stored in a convent easy to reach place that asked to be taken! That was like that for a few years until they tidied the place a few months ago. But Hay, our school makes it easy for use, the new computers they have now are equipped with working DVD-RW!