Thx 
I'm assuming you want to go slightly more legal than "download from Google Image Search" here
http://commons.wikimedia.org/wiki/Main_Page would be my usual source. The pics often aren't great, but they're Creative Commons or public domain.
Alternatively, if you don't mind using Getty's new embed thingie, you could use Getty Images and at least see if they have embeddable pics of the relevant celeb.
Finally, you can of course license them. Unfortunately, celebrity pics tend to be pretty expensive to license, but if you're willing to spend the cash that opens up a lot of great options.
Any stockphoto site, but most can only be used for editorial purposes
http://www.shutterstock.com/blog/200...e-only-images/