There are many others, but these three are probably the largest collections of free images vetted throughly enough to keep you legal.
If you have the right to and are willing to release your book under a creative commons license then you could use creative commons images. Google images has a choice where you can specify images licensed for sharing with a sub choice of images available for creative reuse. About 99.99% of the time the results are creative commons licensed images on flicker.
I was able to gather about 98% of the images I needed by these means.
On Mon, Nov 21, 2011 at 9:04 AM, Chuck Grimes <c123grimes at att.net> wrote:
> They are indeed great photography. But if you want to use them for
> commerical purposes, you got to pay.
>
> CG
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>
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