title_body: Is there an open source video processing/sensor based follow me technology? I'm constructing a multirotor drone and want to introduce follow me feature, are there any open source solutions I can use for that purpose?
  Please note that I want the tracking algorithm to be autonomous based on some video processing and sensors.
upvoted_answer: You may want to take a look at dronecode.org, or their supported projects. Especially, PX4 (which was also mentioned in another answer):
  
  Getting Started with PX4 Autopilot guide
  PX4's Follow-Me Flight Mode
  
  MAVLink's Follow Me plugin
  
  You may also find some interest in some other open sourced drone projects, e.g. ArduPilot's Follow Me Mode. Another one would be DRONEKIT's Follow Me Example.
  If you are interested in NVIDIA hardware, take a look at Redtail - autonomous visual navigation components.