A telestrator is a device that allows its operator to draw a freehand sketch

Sketch (drawing)

A sketch is a rapidly executed freehand drawing that is not usually intended as a finished work...

 over a moving or still video image. The telestrator (or video marker) is most famously recognized in sports and weather broadcasts to diagram and analyze sports plays or incoming weather patterns. The talent typically draws on a touchscreen

Touchscreen

A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus...

 with a finger or uses a pen on a graphics tablet

Graphics tablet

A graphics tablet is a computer input device that enables a user to hand-draw images and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures...

. From the touchscreen or tablet, the drawing signal is communicated to the telestrator, which overlays the video image with the drawing and outputs the combined signal for broadcast or display.

Today, the telestrator is used in a wide variety of applications, from educational, boardroom, church and military presentations to telemedicine

Telemedicine

Telemedicine is the use of telecommunication and information technologies in order to provide clinical health care at a distance. It helps eliminate distance barriers and can improve access to medical services that would often not be consistently available in distant rural communities...

 conferences, where it can be used by both the near and far ends to annotate precise details of microscopic images or other medical images that are under consultation.