To what extent can photos influence people's evaluations of their own knowledge? For example, can photos affect how well people think they understand processes? To answer this question, in six experiments we asked people to indicate how well they understood various processes (such as how rainbows form). Sometimes the processes that were described appeared after a related photo (such as a photo of a rainbow) whereas other times the processes appeared alone. People tended to report that they understood processes that appeared with photos better than processes that appeared alone. This pattern fits with the idea that photos make it easier to generate relevant thoughts and images—an experience people tend to interpret as evidence that they know or understand related information.