<em>The photographer means that the documentary photograph can be served as a thumbnail. Like the videos that we can see in YT, there is a frame that is showing something that would attracts the user to view the video fully. Some includes a short description of the video. The frame is not the whole message of the video but rather a scene or a caption about it. This goes to the documentary photograph. The photograph is not the whole story but rather an excerpt that would interest the user to view or look at the documentary. The larger meaning is the real issue of the documentary, the people behind it and the experiences encountered.</em>
Rather than depend solely upon visual unity, an artist will sometimes create CONCEPTUAL unity by unifying the ideas in a work of art. :) Hope this helps
