Early photographers quickly realized that an image could be worth 1,000 words - and in some cases many more. Words evoke a largely intellectual response from those who read them, but images can produce intense emotional reactions. A good photojournalist harnesses this potential to confront viewers with the reality of pain, injustice or whatever his or her story incorporates. Indeed a successful and factual photo essay has the potential to bring about social change, provoke lawmakers in to changing laws, and even end wars.

An effective and successful essay produces an emotional reaction in the majority of viewers. It may cause them to laugh, feel sad, angry or even walk away in tears. Such reactions are evidence of an author's success. Viewers who walk away unmoved feed back a much less positive message about the success of the work. The best photo essays, like good books and music, tend to stand the test of time. They are still around after countless years, often because the message they convey continues to be relevant even though the events portrayed have long since passed in to history.