While you probably spend most of your time as a photographer thinking about making images, occasionally an editor or commercial client may request your help in finding images — such as historical photos — to illustrate a project. Fortunately, some of the most amazing images ever captured  are freely available; they’re in the public domain.
I’ve written previously about the photographer/entrepreneur Tom Carroll, who “sold” a public-domain image to a corporate client for its annual report for $875. A distinction to note is that Tom did not technically “sell” the image; he located the image for the client and charged a “research fee.”
Government-owned images are generally public domain. When you work for the U.S. government, whether you are building a bridge, landscaping a new park, or taking a photograph, you are working for the people. So, the reasoning is — the people own the results.
I’m surprised that more people have not come up with ways to profitably distribute the photos that are gathering dust in U.S. government archives. Tom Carroll’s approach is certainly valid. We’re already beginning to see stock photo sites leverage the Web to distribute public domain images that are available for the asking.
The case of Public.Resource.Org  is particularly interesting. The group decided that the 6,288 images being marketed on the Smithsonian Images Web site  were actually in the public domain — so they decided to upload the entire collection on Flickr . They are even selling a book containing the images  for $44.
Other government entities are taking the lead in making photos available themselves. This week, for example, the Library of Congress announced a pilot project  to share more than 3,000 photos on Flickr . But because the Library of Congress hasn’t tagged any of the photos (or captioned many), your clients will likely still need help in finding the images they need.
The subjects of government images include aviation (historical to modern, U.S. to Russian); naval (most countries represented); agriculture (historical as well as new and innovative); NASA space photos; and even images from the Central Intelligence Agency, which, believe it or not, are also public domain and available.
The U.S. government cannot own copyright, but even so, not all photographs on “.gov” and “.mil” sites are public domain. For example, a private donor or a foundation might donate a copyrighted image to a federal institution with the restriction that the copyright of the image will eventually revert to the estate of the original owner. The same is true for some photographers who make photos for the government on a “work-for-hire” basis, in which case the images may be copyrighted by the photographer and not the government. If you find an image on a U.S. government Web site, it is most likely usable as a public domain photo, but you’d need to confirm that.
Also keep in mind commercial use of public-domain photos is restricted in ways that editorial use is not. You can learn more about these restrictions here .
If you’re looking for sources of public domain images that have little or no publication restrictions on them, here’s a good place to start .