"A mosaic is the art of creating images with an assemblage of small pieces of colored glass, stone, or other materials to create a pattern or a picture." http://en.wikipedia.org/wiki/Mosaic
The art of making a mosaic is a skilled endeavour and requires plenty of time and patience as well as artistic expertise. It seems to me as if mosaics were an early form photography albeit a slow, lengthy, time consuming version. The concept of the desire to capture an image has not changed but the way in which we can do this has ... think of a piece of mosaic portraying the picture of a person versus a digital photograph. There are still similarities even though one method is old fashioned, laborious and manual whereas the other method is modern, fast and high tech. If we think of the individual small pieces of coloured glass or stone, they are no different than the individual pixels in digital photography. Just as each piece of mosaic is a sample of the original image so too are the pixels and they both help to form an overall picture when viewed as part of a whole image.
Figure 1: A young Tunisian craftsman making a mosaic.