smithsonian on flickr commons
The Smithsonian is putting a collection of public domain photos on Flickr, part of the Flickr Commons project.
Here’s an example, with this curious description:
After parcel post service was introduced [in the US] in 1913, at least two children were sent by the service. With stamps attached to their clothing, the children rode with railway and city carriers to their destination. The Postmaster General quickly issued a regulation forbidding the sending of children in the mail after hearing of those examples.