Film Grain effect: background

I am trying to recreate the film grain effect, and want to use my own image for the grain to appear on, but the marks I draw disappear and end up on the actual “background”. Is there a way to make my image the background so the marks I do draw appear on it, not the original background? I hope this makes sense.


See here for the example I’m after. The tutorial doesn’t mention how to make your image the “background”.