A technique is provided for classifying images in a library (1) for subsequent selective retrieval. Each library image is segmented (2) into a plurality of coherent regions. Each of the regions is analysed in respect of a plurality of visual properties, each of which is ascribed a number according to the value of the visual property. The property numbers are then compared (4) with bands of the available property range and a computer-readable character, such as a letter of the alphabet, is ascribed to each of the property values. The characters are then arranged (5) in a predetermined order to form a region character string. The strings for each region are then indexed (7) to form an index (8) of the images by region character string. For image retrieval, a target image (10) is analysed in the same way to form region character strings which are then supplied to a text retrieval system (12) for detecting matches with entries in the index (8). Library images having matching regions are retrieved from the library (1).