QUICK-COPY YOUR LAYER MASK

If you've applied a Layer Mask to an image, you can duplicate that Layer Mask and apply it to another layer fairly easily. Start by clicking on the layer where you want this Layer Mask to appear. Then, click directly on the Layer Mask thumbnail that you want to copy and drag it down to the Layer Mask icon at the bottom of the Layers palette. When you do this, it creates an exact copy on your new layer.