There are objects and events, both in everyday life and in scientific practices, which we know about not by direct observation but only by means of reports or images. In scientific reasoning especially, we use pictures as surrogates for the objects depicted in them, since we often do not or cannot perceive the objects themselves without technical aids such as microscopes, fMRI and so on. The images yield a specific type of evidence for the existence of the visualized entity that possesses the properties shown. In pictures we trust. We assume that they visualize real features of the depicted objects. But our sources of knowledge have to be credible. We trust other sources of knowledge (like perception or testimony) because we assume that they are able to represent the facts in question and that they usually do so. The use of scientific pictures as pictorial evidence, then, relies on these pictures’ rightness.