Dodgy video - advice please

[Hansel78]

I download porn. Right or wrong, I do, so now that's out there i can get to my point and ask for some advice. Now, I'm more than aware that there are videos out there whose titles allude to paedophile material, but not being one I steer clear of that stuff with a barge pole. But the other night i downloaded a video and in it there's a guy with a white circle covering his face. The girl in the video doesn't look underage to me, but since the quality is not amazing making it hard to determine how old she might be and there's this white circle thing it's played on my mind a bit and I'm concerned the police are going to come smashing through my door at any minute.
How can i report it, and who can i report it to?
How can i stop 'sharing' it?
It baffles me there is stuff available out there like this just floating around but I've always just figured that if there was a way to stop it it would have been stopped, so I've never thought to contact anyone about the titles that you see, but now I've landed with something even dubious I just don't want any involvement in it.