1. A method to detect flaws in the placement of composite tows by a fiber placement apparatus after the tows have been laid up on a substrate to form a composite surface, comprising the steps of: acquiring image data across at least a portion of the laid up composite surface; processing the image data to obtain feature data representative of the location of the edges of individual tows forming the laid up composite surface; and determining the occurrence of flaws in the laid up composite surface using the feature data.