An image processing device outputs, by using a result of machine learning, an image including three or more gradations and indicating a central line in response to an input of a fingerprint image, the machine learning being performed by using data including at least a fingerprint image, central line information indicating a central line in the fingerprint image, and zone information indicating a zone that is a portion of the fingerprint image which is effective for fingerprint collation, and generates a binary central line image based on the output image.