The area of recognising gestures made by humans using computers is generally known as ``gesture recognition''. It is necessary to make a distinction between ``posture recognition'' and ``gesture recognition''. Posture recognition is the recognition of static positions of the body, while gesture recognition must include catering for dynamic changes in posture. Posture recognition is thus a subset of gesture recognition.
Note that there are no bounds on how the posture and gesture information may be obtained -- it need not be hand-based at all, and in general can include facial gestures, body movement and so on. In general gesture recognition is understood to be the recognition of movements and postures that indicate a concept. For example, using a stylus (a computerised pen) for drawing objects would not be gesture recognition. However, if you were to use that stylus to ``cross out'' a drawing, indicating that you didn't want it, and the computer would recognise this as an indication of that fact, that would be considered gesture recognition. Recognition of sign language is a specific example of gesture recognition. So far, since sign languages tend to be manual in basis (although they are not exclusively so, and typically also include a component of facial gesture), most research in this area has focussed on measuring hand movement, and basing recognition on this, using one of a variety of approaches. Some work, however, has been done at recognising signs at a body level.