A video detection system detects the edge line of a microcircuit component that is to be trimmed by a laser trimming apparatus. The components (46, 48, 50, 52) to be trimmed are darker than the substrate (44) upon which the components are formed. The system generates a video signal corresponding to the image of the part (26) that carries the circuit. The brightness level of a selected point in the video signal is monitored. The position of the selected point corresponds to a point on the part image and is adjustable to be aligned with the point where the laser beams (24) contacts the surface of the part (26). The image is moved relative to the selected point, and as the edge of the relatively darker component to be trimmed crosses the selected point, the corresponding change in the monitored brightness level provides an indication that the edge of the component has been detected. Also provided is an alignment symbol for superimposition on the displayed image. The selected point (90) is incorporated into the alignment symbol. The alignment symbol is preferably cross hairs (88). The symbol brightness level is automatically adjustable to contrast with the brightness level of the portions of the part image over which the symbol is superimposed.