For the last six months, I have been getting at least three phone calls or emails a week from clients, all of whom run legitimate businesses with robust websites, and all of whom have gotten letters from photographers (mostly their representatives) seeking licensing fees for photos that have been posted without permission. Many of these photos have been on these websites without incident for years.
For a long time now, people have generally felt it appropriate to go onto various image search engines, find a photo for a newsletter, website, or other publication, and then cut and paste it into their publication or website. This trend did not generally apply to hard copy publications, because when you cut and paste something from the internet, the quality is not sufficient to reproduce in hard copy, as it pixilates and becomes distorted. However, because of the limited resolution of computer monitors, a cut and pasted image looks perfectly fine when copied to a website. As a result, based on ignorance of copyright law, believing in the myth of "it is on the internet so I can use it," or simply thinking the chances of getting caught were so minimal that it was worth the risk, hundreds of thousands of images have probably been cut and pasted without license and put on third-party websites and on-line publications.
One of the reasons this was so easy to get away with in the past was there was no effective way for photographers to find unlicensed uses of their work. When you went onto the various search engines' image sections, what they were doing was searching for text surrounding images and offering up all sorts of related and unrelated images. A search of "Ronald Reagan" would result in pictures of Ronald Reagan, the Ronald Reagan Building, Ronald Reagan Airport, Ronald Reagan Highway, etc. Recently, photographers, wire services, and photo agencies large and small have either acquired new technology or engaged search companies that have image searching technology. These types of entities are now searching for images themselves. If you would like to see an example of how this works, you can go to www.tineye.com and upload an image (it's free), and you will see instantly how it scours the open internet, finds every use of the image, and gives you the website attached to it.