Fluid Composite Rendering (FCR) uses state of the art 3D modeling tools to develop suspect composite sketches.  This highly interactive and responsive method allows unlimited, instant iterations and modifications to a base head.  The 3D head model can be sculpted, pushed, and pulled endlessly until those certain unspoken, intangible qualities that make a particular face unique eventually emerge.  Also perfect for building up a likeness from captured video footage or still images.  The link above is a short demo describing Fluid Composite Rendering.