Images now play a crucial role in fields as diverse as medicine, journalism, advertising, design, education, entertainment, etc. Technology, in the form of inventions such as photography and television, has played a major role in facilitating the capture and communication of image data. But the real engine of the imaging revolution has been the computer, bringing with it a range of techniques for digital image capture, processing, storage and transmission through internet. The creation of the World-Wide Web in the early 1990s, enabling users to access data in a variety of media from anywhere on the planet, has provided a further massive stimulus to the exploitation of digital images. The number of images available on the web was recently estimated to be between 10 to 60 million , which some observers consider to be a significant underestimate.