Scanning is basically taking a close-up photograph (just very slowly and with great detail). The scanned image data is passed to the computer.
The most common type of scanner is the flat-bed scanner which has a glass plate on which the item to be scanned is placed. The item is illuminated and an image of it is captured by a moving scan ‘head’.
Scanned images can be further processed once inside the computer, e.g. OCR of printed text.
Most digital cameras do not directly input data into a computer - they store photographs on memory cards. The photographs can later be transferred to a computer.
A modern digital camera can capture 10 Megapixels or more per photograph - that’s 10,000,000 coloured dots (pixels) in every photo!
Like a digital camera, most video cameras do not directly input data into a computer – the captured movies are stored on video-tape or memory cards and later transferred to a computer.
However, there are some situations where video cameras do feed video data directly into a computer: television production and video-conferencing. In these situations the video data is required in real-time.
The video data from a web cam is low quality compared to a full video camera. However it is good enough for web chats (e.g. using a messenger application such as MSN Messenger or Skype).
Usually a web cam is clipped to the top of a monitor, but many laptops now have web cams built into the edge of the screen.
The signal from a microphone is usually analogue so, before it can be processed by a computer, it must be converted into digital data. An Analogue-to-Digital Convertor (ADC) is used for this (usually built into the computer’s sound card)