Human visual perception is excellent in detecting shapes of objects. Even small children will easily differentiate between circles, squares or triangles when wooden toys or sweets are at stake. Similarly, machine vision applications on the factory floor or in the open environment sometimes call for quantitative parameters to characterize a shape. Traffic signs, e.g., may well be pre-classified by their shape, and for some pills the integrity of their shape is an important issue in quality control. This article describes some simple, well-known methods of shape detection.