A method for validating the placement of pieces in an assembly task by scanning a coherent light source, such as a laser, over a surface and characterizing the detected interference speckle pattern to discriminate the position of the placed piece from the surface on which the piece is placed. This discrimination is possible even if the characteristic features of the piece and background are smaller than the resolution of the scanning system. In addition, characteristics of the piece, such as the orientation of fibers in the material, may be sensed by classification of the associated speckle response.