[Creating photo collage with vignettes]

I have been searching and searching and can't find a way to do what I want to do.  I am making a photo collage with 10 different photos and I want a simple black vignette around each individual photos to separate them. When I created a vignette on each individual photo by selecting the area I wanted, inverting the selection, and then creating a brightness contrast layer it worked on the individual picture. However, because the photos are all different sizes in my collage, when I added them to the collage the vignettes were then all different sizes as well.  So I made my collage without the vignettes thinking I could do that same thing on each layer, but when i select the inverse, it obviously selects the rest of the entire collage. So, I created a vignette for the outside of my 16x20 collage. Is there a way to copy that vignette so I can use it around the individual photos in the collage as well? Or is there a different way I should be trying? Thanks.