1. An object recognition system comprising, means for effecting relative movement between an object and a viewing position, means for deriving image data representing a plurality of images of the object taken from different viewing directions which are angularly disposed about the direction of said relative movement, data compression means for compressing the derived image data representing the image taken from each said viewing direction, a source of image data arranged to provide image data representative of images of the object taken from a plurality of reference viewing directions which are angularly disposed about a reference line corresponding to the aforesaid direction of said relative movement, the angular separation of said reference viewing directions being small in relation to the angular separation of the first mentioned viewing directions, and correlation means for comparing the compressed image data with image data from said source to produce an indication of which image represented by said derived image data has the highest correlation with any one of said reference images, so that the orientation of the object can be determined to an accuracy related to said relatively small angular separation.