Are you scaling the images down (smaller)? if so I would do scaling in Photoshop first because if you scale down a large image in After Effects the image may have artifacts (such as jittery fine lines).
You should “pre-comp” your images first. To do this place your 1 image in a composition and scale the image. Then place that composition inside another composition. And repeated:)
BUT, I assume you have already scaled your images and they are all in one composition.
If so…simply click and select a layer and from the top menu select> Layer > Pre-compose.
Doing this places the layer in its own comp.
It will ask if you want your “attributes” (scale, transparency, rotation etc) moved to the new comp as well.
IF the images are scaled already, Choose “move all attributes to new comp”. After this, there will be a composition where the image once was and the composition will be at 100% scale so your masks will also be at 100% scale.
If this is not helpful then
Im not sure if I understand you exactly.
OR I don