Testing Theory: Academic Studies You’ll Actually Use is a series that provides practical testing ideas based on the study of how people make decisions (formally known as behavioral economics).
Photos have the power to greatly influence conversions and engagement, but testing them is tricky. There are so many potential images you could be using, how are you supposed to know which ones are likely to have a big impact? For example, how did the Obama and Romney 2012 campaigns decide to use the images below on their donate pages?
One concept that can guide you to find the ideal image is priming.