Abstract: A security screening system to determine if an item of luggage carries an object posing a security threat. The security screening system may comprise an input for receiving image data derived from an apparatus that subjects the item of luggage to penetrating radiation, the image data conveying an image of the item of luggage. The security screening system may also comprise a processing module for processing the image data to identify in the image a plurality of regions of interest, the regions of interest manifesting a higher probability of depicting an object posing a security threat than portions of the image outside the regions of interest.