1. An image processing device comprising: a processor comprising hardware, wherein the processor is configured to: identify an identified image selected according to a first user input operation received by an input device, from among a plurality of first images acquired by a capsule endoscope; identify a plurality of second images acquired by the capsule endoscope, each of the plurality of second images being captured at a position within a predetermined position range from an identified image capsule position where the identified image was captured by the capsule endoscope, from the plurality of first images; acquire an imaging sequence of the plurality of second images; acquire a plurality of capsule positions, each of the plurality of capsule positions being a position of the capsule endoscope when each of the plurality of second images is acquired; determine from the imaging sequence of the plurality of second images and the plurality of capsule positions whether the capsule endoscope engaged in a reciprocating movement during the time period in which the plurality of second images were acquired by the capsule endoscope; in response to determining that the capsule endoscope did not engage in the reciprocating movement, set the identified image as a feature point image; and in response to determining that the capsule endoscope did engage in the reciprocating movement: extract a plurality of candidate images in a first forward path or a last forward path of the reciprocating movement from among the plurality of second images; and set an image selected according to a second user input operation received by the input device, from among the candidate images, as the feature point image.