And specifically, what circumstances led to a political cartoon being the most relevant image, as opposed to an actual photograph or a realistic (non-caricature) drawing? I could understand New York scandals being big news in Europe, or American authorities alerting their Spanish counterparts to be on the lookout for Tweed, but I would expect both of those to result in actual pictures of Tweed. Why a political cartoon?
Certain people from various parts of the world seek knowledge from various sources. A cartoon is one of the easiest methods to glean knowledge because of pictorial references that transcends culture and background. For example, early on I learned science from reading enlightened comic book authors.