[kmoser]

"My" is used to make it clear that it contains the user's pictures, not pictures from other people, Apple, the Internet, etc. Just "Pictures" would make it more ambiguous. (Not saying it's the right thing to do, just pointing out why they do it.)

[hahn-kev]

If that's the case then there should be another folder to put pictures that aren't mine.

[toast0]

In Windows, with the right settings, you might have a 'Shared Pictures' folder or a 'toast0's Pictures' folder.