Concurrently, digital photography took off. “It used to be you really needed to know how to use a camera,” said Keith Marlowe, a photographer who has worked for Spin and Rolling Stone. “If you messed up a roll, you couldn’t redo the concert.” Now, though, any photographer can instantly see if a shot is good, or whether the light balances or other technical aspects need to be adjusted.

That meant a flood of pretty decent photographs, and that changed the stock-photography industry. In the last few years, stock agencies have created or acquired so-called microstock divisions. They charge $1 to $100, in most cases, for publishers or others to rerun a photo, often supplied by an amateur. And Getty made a deal with Flickr in 2008, permitting Getty’s photo editors to comb through customers’ images and strike license agreements with the amateur photographers.

Image "Adventures in Childhood" is under a royalty free license with Getty Images. Credit... D. Sharon Pruitt

“The quality of licensed imagery is virtually indistinguishable now from the quality of images they might commission,” Mr. Klein said. Yet “the price point that the client, or customer, is charged is a fraction of the price point which they would pay for a professional image.”

In 2005, Getty Images licensed 1.4 million preshot commercial photos. Last year, it licensed 22 million — and “all of the growth was through our user-generated business,” Mr. Klein said.

That is because amateurs are largely happy to be paid anything for their photos. “People that don’t have to make a living from photography and do it as a hobby don’t feel the need to charge a reasonable rate,” Mr. Eich said.

With stock-photography payments declining and magazines pulling back on original assignments, some Web sites like Life.com and BurnMagazine.org have popped up as homes for original photography. Life commissions about two projects a month — it sent Mr. Marlowe to Haiti after the earthquake, for instance, and the entertainment photographer Jeff Vespa to cover the European news media tour by the “Avatar” cast.