What Am I Allowed To Do With Screenshots?

Hi, I know I am probably in the wrong area doing the wrong thing...but I was just wondering what is deemed "acceptable" when uploading screenshots to either Facebook or another non-profit website - And what happens if I do not know who created the car within the screenshot I have taken?

 

In terms:
You can upload the screenshot anywhere on the internet as long as it's not for a profit, and you ask for the creator's permission.
But if it's your own screenshot, go ahead, do anything you want with it.