“New Old Stock” is a website, hosted on tumblr, featuring handpicked publicly available stock photos from the past, curated mostly from Flickr accounts of various institutions. All of those a free to use in general, but might require some sort of attribution. Photos from Flickr on New Old Stock are always linked to their source so it’s pretty easy to find the actual copyrights and use restrictions of a given photo.
Here’s an example:
Being a Tumblr-hosted website, it uses a theme that does not provide or is not configured to display a search form, so searching a specific image is probably easiest done on Flickr’s search engine or even Google Images. Yet, if you’d like to roam across an endless list of vintage photos that you might be allowed to use in your own projects, this might be a good fit for you.
Licensing for provided images: various
Registration required: no
Handy search and filtering: no
Here’s a link to the site: New Old Stock