how to prevent others to use my dll and ocx?

I was amazed when I tried to use an ocx and a dll from a program for capturing image from webcam. As I tried to use their ocx and dll in the reference of my project, I cannot add it as reference because it prompt that I dont have a license to use it on design mode.

It got my interest there because its first time that I know that.

So I would like to ask how was it possible? how was the dll and ocx made that it prompts of a message when like I dont have such license.