The site contains a lot of great information, albeit with a few inaccuracies (for example, the FAQs at one point seem to imply that all photographs are under copyright, which isn't true). Needless to say, the site also encourages image users to license their images from stock photo agencies such as Getty Images. That said, the good thing about licensing through Getty Images and similar agencies is that they will tell you whether or not a model release has been obtained for a particular photo and the purposes for which the photo can be used, and, in the event that they failed to obtain the permissions that they promised they obtained, they will indemnify you if you get in trouble as a result (i.e., they will foot the bill).
The video below, from the site's homepage, explains the various rights that different people may have with respect to a single image: it is necessary that permission from all rights holders be obtained before using an image.