A welding system in which a welder automatically tracks the seam to be welded. This is an automatic servo-driven tracking system employing a raster-scan television camera as an optical sensor. The camera is aimed at the seam area in advance of a cross-slide mounted welding head with the line scan substantially perpendicular to the seam. The camera produces a voltage pulse which exactly coincides with the point in time at which the line scan intercepts the seam. The time incidence pulse is referenced to the standard synchronization pulse (the initiation of the line scan) of the camera. The video signal line which contains these pulses is fed to a novel video anomaly detector. The detector processes this information and produces an output voltage which is analogous to the position of the seam. This output is directed to a master/slave position servo drive system which maintains the welding torch over the seam as the seam moves past the welding station. The image produced by the television camera may be displayed on a conventional television screen together with a line indicative of welding torch position for visual observation of system operation.