In an image processing apparatus 2, images of a subject object 210 and data defining the positions and orientations at which the images were recorded are processed to generate a three-dimensional computer model of the subject object 210. As part of the processing, image data relating to the subject object 210 is segmented from other image data in each input image. The results of the segmentation processing are displayed to a user and the apparatus is operable by the user to edit the segmentation processing to correct any errors. Such errors typically occur due to the misclassification of pixels relating to shadows in an input image as part of the subject object 210 and the misclassification of pixels relating to features on the surface on which the subject object 210 is placed for imaging as part of the subject object 210. The facility to edit the image data segmentations therefore provides the user with greater flexibility in the lighting conditions which can be used for imaging and greater flexibility in the selection of the surface on which the subject object 210 is placed. The results of the segmentation processing, including any edited results, are used to generate a three-dimensional computer model of the subject object 210.