The identification of an individual machine is made possible through the observation of defects which are reproduced on the resulting copies. The most common of these defects are called "trash marks" and are more often the result of dust and dirt particles. These particles are seen as black specks on a copy and can enable identification of one copy with another if the size, shape and groupings of these marks are comparable between the two copies. Defects can also be the result of rollers and other parts of a particular machine.