1. A method of calibrating a geometric model of a fingerprint imaging system, the geometric model defining the geometry of reflective and/or refractive surfaces associated with optical elements within the fingerprint imaging system at which light is reflected or refracted, the geometric model including a plurality of surface parameters that define the positions of reflective and/or refractive surfaces within the fingerprint imaging system in relation to other reflective and/or refractive surfaces within the fingerprint imaging system, the method comprising: capturing an image of a predetermined target with the fingerprint imaging system, the target including distinguishing points provided at predetermined positions on the target; measuring positions of the distinguishing points in captured image of the target; comparing the measured positions of the distinguishing points in the captured image to positions of the distinguishing points predicted according to the geometric model of the fingerprint imaging system, wherein comparing the measured positions of the distinguishing points to the predicted positions of the distinguishing points comprises determining a value of a metric function for the surface parameters, and wherein the metric function describes an accuracy of the geometric model in predicting the positions of the distinguishing points in the captured image of the target as a function of the surface parameters; and adjusting the surface parameters of the geometric model that define the relative positions of reflective and/or refractive surfaces associated with optical elements in the fingerprint imaging system based on the comparison between the measured positions of the distinguishing points and the predicted positions of the distinguishing points.