Optical contrast seekers, or simply contrast seekers, are a type of missile guidance system using a television camera as its primary input. The camera is initially pointed at a target and then locked on, allowing the missile to fly to its target by keeping the image stable within the camera's field of view.

The first production missile to use a contrast seeker was the AGM-65 Maverick, which began development in the 1960s and entered service in 1972. The system has not been widely used, as other guidance technologies like laser guidance and GPS have become more common, but the same basic concept is used in cameras to track objects, including the systems used to aim the laser designators.

Contrast seekers should be distinguished from television guidance systems, in which a live television signal is broadcast to the launch platform, which then uses manual direction to attack the target. Examples of TV guidance include the Martel and AGM-62 Walleye. The term "contrast contour" is sometimes used, but this may be confused with TERCOM systems.

Analog television cameras scan an image as a series of horizontal lines that are stacked vertically to form a grid or "frame". The camera's progression through the frame is carefully controlled by electronic timers, known as time base generators, that produce smoothly increasing voltages. As the camera scans the image, the brightness of the location currently being scanned is also represented as a voltage. The series of varying voltages from the sensor forms an amplitude modulated (AM) signal that encodes the brightness variations along any given scan line. Additional voltage spikes are added to the signal to indicate when the line or frame ends.

The contrast seeker is a simple device that can be implemented using basic analog electronics. It first uses some form of automatic gain control to adjust the image brightness until it contains some areas with high-contrast spots. This produces a bias voltage signal to represent the background brightness level, making brighter objects stand out. Any rapid change in contrast along a given scan line causes the voltage from the camera to suddenly change. If the change is greater than a selected threshold, it triggers a second circuit that sends the output of the two scanning time base generators into capacitors. Thus, the capacitors store a voltage value representing the Y and X locations of any high contrast spot within the image.

The image from the missile's camera is also sent into the cockpit where it appears on a small television screen, often one of the aircraft's multi-function displays. The missile is initially brought onto the target manually, normally using a small cueing input on the pilot's control stick, or by the weapons officer in a two-seat aircraft. When the trigger is pressed to pickle the target, the contrast threshold circuits are turned on when the camera is scanning locations close to the pickled location on the screen. Any high-contrast images within that area will then be memorized. Normally the recorded spot is indicated on the screen, normally with a square around the selected location. The operator can select other high-contrast spots within the image in an attempt to select one that is either on the target or very close to it.

Once a suitable target image has been selected, the seeker enters tracking mode. In this mode, the output from the camera is ignored except when it is scanning close to the original pickled location. In those locations the circuit triggers as normal, sending the output to a second set of capacitors. By comparing the voltages in the two sets of capacitors, the difference in location between the originally selected spot and the current spot is output as an error signal. This is sent into the seeker's gimbal mounting to turn the camera so it re-aligns with the original location. The guidance system then compares the angle of the camera to the angle of the missile body and sends commands to the aerodynamic controls to bring it back onto a collision course. To address the need to track moving targets, a proportional navigation system is normally used, which naturally produces the required lead.

Contrast seekers are subject to problems when the contrast spot changes. This can occur quite easily if the target changes angle, causing the absolute brightness of the object to change, or if it moves, which can change the contrast relative to the surroundings. For instance, a tank on a roadway might provide a very high contrast tracking spot, only to have that disappear when it drives off the road into low bush. It can also be fooled by artificial lighting changes and similar effects. This is the reason that the timers are "gated", to limit the area in which the changes can take place without breaking lock.