A system to identity at least a property of a substance located in an object, or located on a surface of the object, is generally described. The system may include an electromagnetic radiation (EMR) source arranged to selectively emit EMR at more than one wavelength to illuminate the surface of the object. The system may include an EMR sensor arranged to sense EMR returned from the surface and to use the returned EMR to provide an output signal that represents an image taken of the surface, the image including a plurality of pixels. The system may include a processor system arranged to compare information that is indicative of the output signal of the EMR sensor with reference information indicative of the property of the substance. The processor system may be arranged to select a first wavelength to illuminate the surface by the EMR source, and subsequently select at least one further wavelength based on whether the information concerning the property is obtained as a result of use of a preceding wavelength. The processor system may be arranged to compensate fur an influence of ambient light on the at least one surface, and may be arranged to compensate for motion of the object relative to the EMR sensor.
