Doctors in hospitals use X-ray pictures to check for broken bones.
Meteorologists employ images from satellites to help forecast the weather.
Law enforcement officers study aerial photographs to find out where drug crops are being grown. Recently we have been amazed by the images of the planet Mars from the Pathfinder mission and by other astronomical images from the Hubble telescope. Many images from these projects can be found on the web. Images are often displayed on a computer screen as a grid of picture elements called pixels, with each pixel having assigned to it a particular colour or shade of grey. An ultrasound image of a cross-section of the head of a human foetus.