Duplicating A Layer Mask in Photoshop
When working with graphics and photos that contain layer masks, adding new layers and duplicating the mask is a quick and simple process.
Start with a layer mask. As shown below, the masked layer is "feed."
Add content to be masked. Add the new photo to the layer above the masked layer, as shown below.
Hold "alt/option" while dragging the mask to the new layer. This duplicates the mask instead of moving it.
New layer mask complete. As shown below, both layers are now masked.
