1. A method of determining data characterising a set of images of an object, the method comprising: inputting data from a first set of images of said object captured from a plurality of different positions; determining frontier point data from said data for said first set of images and data defining said image capture positions, said frontier point data defining a plurality of frontier points on said object, and for each said frontier point, a direction of a normal to the surface of the object at the frontier point; inputting data from a second set of captured images of said object, said second set of images having substantially the same viewpoint and different illumination conditions; and determining data characterising said second set of images using said data for said second set of images and said frontier point data, said image set characterising data comprising object reflectance parameter data (β) and, for each image of said second set, illumination data (L) comprising data defining an illumination direction and illumination intensity for the image.