Collage is one of my favorite mediums and I often use vintage images when creating work, usually beginning with a base of my own photography. But copyright is always a concern so I’m very careful to make sure all of my images come from the public domain. One of the best resources I’ve found is the New York Public Library’s digital collection. The images are great quality, downloading is easy and no additional permission is needed for use.
Here’s the link: http://digitalcollections.nypl.org/
And a few collage pieces I worked on today with some of the images. More HERE