Everyone has the right to control his image.
And there are [international] rules for copyright of intellectual or artistic works.
If you put photographies of somebody on your site, you must ensure that :
1. You have the right to do this (this is the case if you took the picture yourself)
2. The person must agree to have his image on the site. Usually, to prevent any problem, it's a good idea to print the photo on a paper and ask this person to write down that he agrees the publication of this image on your site (+ date, of course).
3. [optional] If 1 and 2 are ok : you should clearly mention that you are the copyright holder of the picture.
Hope this helps...