Create a square frame for camera

Hi everybody,
I need to create a square frame in the middle of a camera view something like that :

Any Idea of how i could do it ?
Thanks for answers.

See:

2 Likes

Thanks robinyo.Lemme check it.

Robinyo,
I saw this plugin is not open source so I have to pay a license. Do you have of how i could get the same result for free ?