Customer computer processing apparatus (2, 4) are connected to a service apparatus (6) via the Internet (8). Service apparatus (6) processes requests and payment details from a customer apparatus (2, 4), and, in response to a valid payment, sends instructions to the customer apparatus to enable the customer apparatus to control a printer (18) or a display panel (19) to print or display a photographic mat (24). Service apparatus (6) retains details of the photographic mat pattern for subsequent use. Images of a subject object on the photographic mat are recorded at different positions and orientations with a camera (16). Data defining the images is returned from the customer processing apparatus (2, 4) to the service apparatus (6). The service apparatus processes the image data along with the stored pattern data to identify the photographic mat features in the images and to calculate the position and orientation at which each image was recorded. A three-dimensional computer model of the subject object is then generated using the calculated positions and orientations.