1. A device for processing an image, comprising: processing circuitry configured to receive image data of a pixellated current image, and to determine from that image data at least one parameter indicative of the characteristics of an illuminant, wherein the illuminant is the source (or sources) of light of the image; the processing circuitry further configured to process the at least one parameter indicative of the characteristics of the illuminant to derive illumination data indicative of the spectral characteristics of the illumination of the scene shown in the current image, and to process the image data using the derived illumination data thereby to determine the spectral reflectivity of at least one surface of at least one object shown in the current image by deriving at least one parameter representative of said spectral reflectivity; modelling circuitry configured to derive a background model from information of at least one previous image of the scene; and decision circuitry configured to compare, over a wide spectral band said spectral reflectivity with a spectral reflectivity of a part of the background model, the comparing performed by computing a similarity measure by combining the at least one parameter representative of said spectral reflectivity with at least one parameter indicative of a similarity between spectral basis functions.