A method for operating an accessory device to capture calibration data. The method can include capturing an image of a portion of a user's body that includes the user's stoma and at least two reference locations, and storing distance scale information representative of a distance between the two reference locations. The method further includes processing the captured image, including: identifying the reference locations, identifying the stoma, and generating calibration data representative of one or more stoma parameters as a function of the identified reference locations, identified stoma and the distance scale information. The calibration data can be stored.