The use of photographs throughout the text is intended to elicit an emotional response from Riis's readership. He is quite literally showing them, through the use of incontestable visual evidence, "how the other half lives." This proves a convincing means of persuasion through emotional appeal, or pathos.
While the phrase has become cliché, it is undoubtedly true for Riis that, in creating How the Other Half Lives, a picture is indeed worth a thousand words. More so often than written language, an image can provoke the viewer to respond emotionally to the suffering of others. And this, in turn, might push them toward taking some sort of action. This is of particular importance given that much of Riis's domestic readership, not to mention his international readership, would likely have never seen the tenements in New York City before picking up How the Other Half Lives.
The use of photography also plays a critical role in establishing Riis as a credible journalist, contributing to the ethos of his text. Words can be used to cleverly embellish a situation, but pictures cement Riis's words as true, or, at the very least, help him emphasize the severity of the problem. As a social reformer, Riis did not want to settle for simply describing the problem, he wanted to fix it. The pictures are a necessary element of his argument, establishing credibility and provoking an emotional response to spur people into action.
