In the US we have some fair use exceptions that allow one to reproduce or closely reproduce the work of others to a limited extent. For example, I can copy a passage from a copyrighted book. I can't copy the entire book.
Does anyone know to what extent that right extends to copyrighted photographs?
Case in point, Google supplies pages of thumbnails of copyrighted images that link back to the posted version. That must be legal?
Yes, fair use applies to photographs.
There was a lawsuit a few years ago against a search engine (not Google) that indexed images. The court ruled that the thumbnails were fair use, after evaluating the four factors that determine whether a use is fair (see [a href=\"http://www.copyright.gov/fls/fl102.html]the U.S. Copyright Office fact sheet[/url]).
OTOH, if you clicked one of the thumbnails, it brought up the full-res image. The search engine had an interesting argument on that one: We didn't actually copy the image, since the <img> tag on the page fetched the image from the original source, not from a copy on our server. And since we didn't make a copy, it can't be a copyright violation.
But the court ruled that copyright covers not only the right to reproduce
a copyrighted work, but also the right to display/perform publicly, and so the act of displaying the original image was covered by copyright law, after all. The company lost that part of the case (the court found that displaying the full-size images wasn't fair use).