A device that captures a text document or an image and converts it into a digital image is called a scanner. Two types popular scanner are handheld scanners and flatbed scanners. The flatbed scanner is more popular now a day.
A flatbed scanner has a glass pane. When the images are placed on this pane, a bright light illuminates the pane and the scanner head moves across the image. It reads as a series of light and dark spots. Only charge coupled devices can see the image because the light is reflected on that device. If the image is transparent then flatbed scanner can not work, it requires special accessories that illuminate them from the upper side.
Handheld scanners work like a manual device. When the scanning starts, it drags across the surface. It has a start button which is held by the user for the scanning duration. Some handheld scanners also have a small window that use for scanning the document.