I think it would be risky to depend on fair use in reproducing photographs for which you do not have copyright. All four factors have to be evaluated (purpose and character of use; nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for the work). As Ron points out, you might get by with it, but you might not. Other factors come into play, including how much effort you have put into searching for the copyright owner. This should be documented. And there are special considerations in regard to digital images.