If you need to apply the same mask to multiple layers, you can copy it from one layer, select the layers to paste to, and then paste. The mask will be pasted into all selected layers.
Or you could save the mask as an animation preset, select all layers, and then apply the animation preset to all of the selected layers.
I relize that but all the images are different sizes. I should have noted that in the original question. Thanks
...the images are different sizes...
Then you'll have to go with a much-more complicated Plan B: paste the mask to a solid, duplicate the solid enough times to match the number of layers, and use these solids as track mattes. If your layers move, don't forget to parent the solids to them.
I would like a stroke around all the image in my comp. To do this a mask needs to be applied to each layer. I currently use the ctr-shift-n short cut & ctr-down arrow over and over. With a 100 or more images it's a pain. If I select all layers I cannot add a mask. Anyone know of a way to do this? Thanks
Why does the mask need to be applied to each layer? That's not reasonable in most workflows. You should be looking for ways to avoid doing that, not trying to hack a solution to a problem you should not have.
Why ca't you precompose the whole thing and apply a mask to an adjustment layer?
To the same effect, you can:
1. Precompose the images that need masking,
2. Apply the mask to a solid layer below all the images
3. Click the "Preserve Underlying Transparency" checkbox (the one in-between "Blending Mode" and "Track Matte" drop-downs) on all the image layers above it.
Just another option.
Like bogiesan said, you should avoid making the problem any more difficult than it has to be.