Images can be formed with many kinds of signals, including ultrasound (high frequency sound waves) and all parts of the electromagnetic spectrum.
Images can be recorded electronically by micro sensors, a very important example of this is the charge-coupled device CCD variations of which are used in web cams and digital cameras.
Images now can be recorded on an atomic scale using electron microscopes and scanning tunnelling microscopes.
Images can be stored digitally as an array of pixels each defined as number. To understand this further information may be needed, pixels are the tiny building blocks from which a digital image is built, each pixel (picture element) when looked at by the human eye blends together to form an entirety of a picture. Although an image may appear to have continuous data however it is discreet data, all too close to be detected normally. The more pixels a picture for a certain part the higher the quality or the lower the resolution.
The resolution of an image is the scale of the smallest detail that can be detected in the image. In digital images every pixel is stored as a group of binary digits or bits, the higher the number of bits per pixel the more different colours that can be showed. A bit is the smallest unit of digital information, represented as a 0 or a 1 corresponding to low voltage or high voltage in a digital circuit.
In all images there is a trade-off that is carried out between quality (resolution and bits per pixel) and the size of the image. Quality is important, however if the image is too large it may too long to load or to transfer. To reduce the size of an image different types of compression are used, these can range from only sending the parts of the image that are changing, or by using grouping large sections that have the same colour. In this way the quality can remain the same but the size decreases. If an image is compressed it is important for both the receiver and the transmitter to know how the compression will be carried out, and also if too much compression is carried out it may again increase the time to actually display the information as the image will have to be decompressed.
Various techniques can be used to manipulate an image. Averaging can smooth images, and locating edges can sharpen them (by increasing the dominance of edges). These techniques are far ranging and complicated, and it will really depend on your particular course on what you will have to learn. You may just have to know that images can be manipulated and nothing else.