An image processing apparatus includes a controller programmed to receive image data and also receive, from a user, an input number of separators included in the received image data. The controller detects a number of times a separator is included in the received image data based on criteria for detecting the separator, and determines, based on the detected number of times and the input number of separators, whether the criteria needs to be modified. In response to determining that the criteria needs to be modified, the controller modifies the criteria for detecting the separator and repeats detection of a number of times the separator is included in the received image data based on the modified criteria for detecting the separator.