Your business clients know it, instinctively if not empirically - there are many good reasons to use photos in their ads and catalogs and on their web pages - photos capture attention better than bold headlines, they add visual interest, and, as they say, a picture is worth a thousand words and is efficient at conveying the message where space is limited and expensive. But as effective as photos can be, today's business models for licensing third party photography are sufficiently complex enough that it's worth taking a few minutes to review the basics and get familiar with the terminology so you can best advise your business clients.
You've already done a lot of work: creating your requirements definition, identifying and qualifying prospective vendors, evaluating their proposals, selecting a winner and doing your due diligence, negotiating refinements to their proposal. But before you sign the vendor's form agreement, be sure and measure it against this list of common shortcomings that can, if not corrected, leave your expectations unfulfilled.
I'm something of a collector.