in answer to the thread starter, nope, they're not stock photos. Apple has them specially shot for using them as demonstrative samples for albums.
But they're aren't pictures taken by Apple employes neither as it would employ a lot of privacy matters. moreover they're not random photos of people because since they're used to demonstrate Apple software such as iPhoto, Aperture, or the iOS photo albums, they're shot by professional photographers to achieve a look that is qualitatively perfect while maintaining a sort of "random" visuals to make it seem like they were effectively taken by the people you actually see in the albums doing trips, as they would have created an iPhoto album.
The people you see in the pictures are models or specific people that got paid for being portrayed in determinate situations (i.e. a family doing a family trip, or a group of friends traveling etc.) and for example they offer to a family or to a group of young people to get paid for a free trip or an adventure provided that they got photographed and give the permission to use their image as samples for Apple.