PicFindr lets you search many photo sites simultaneously and, in addition to defining the image you want, you can define the restrictions for use. For example, I typed in that I was looking for a picture of a lion for educational use, checked the “none” box for licensing requirements (which means anybody can use it — even without crediting the photographer) and got several hundred images to choose from.

I’m adding it to The Best Online Sources For Images list.

Thanks to The Make Use Of blog for the tip.