Microexpressions can be difficult to recognize, but still images and video can make them easier to perceive. In order to learn how to recognize the way that various emotions register across parts of the face, Ekman and Friesen recommend the study of what they call "facial blueprint photographs," photographic studies of "the same person showing all the emotions" under consistent photographic conditions.[18] However, because of their extremely short duration, by definition, microexpressions can happen too quickly to capture with traditional photography.