I had a question in my email by a new scrapper on how to use filmstrips. I was going to make some pics to go along with it but I am swamped today, just taking a break from the cleaning to do a little email catch up.
Anyway, if you don't crop or can't crop your photo small enough to avoid it showing through the holes then take some matching paper, ribbon or the shape tool and place it just underneath the filmstrip. I add this before I add photos and group the film with the "undercolor" so I don't accidentally misalign them.
Tip: Zoom in on your edges to make sure your undercolor and photos are not sticking out into other photos or into the layout.
When I have items overlapping the edge of the page, I use a white box and cover the edges so I end up with that white border around my layout.