Page 240 - Photoshop for Lightroom Users – Scott Kelby 2nd Edition

Step Eight:
Whether you used Paste in Place, or you had to use the Auto-Align Layers feature to get both layers perfectly aligned, at this point, they’re aligned. So,
click on the top layer to make just that layer active, then press-and-hold the Option (PC: Alt) key and click on the Add Layer Mask icon (the third icon
from the left, circled here in red) at the bottom of the Layers panel to hide the top layer (the one with Erik’s eyes fully open) behind a black layer mask.
Now, get the Brush tool (B) from the Toolbar, choose a small, soft-edged brush from the Brush Picker up in the Options Bar and, with your Foreground
color set to white, paint over Erik’s face (well, that general area). As you do, it reveals the “eyes open” version of him on the top layer (as shown here), and
your group shot has everybody looking good.