So, using your pen tool, start anywhere on the part of the scan you want extracted. I started right at the left shoulder, as you can see (our left, her right, obviously). Go all around the part you want extracted, hence:
See where I started and ended?
So, now that you've gone all around, close the path by clicking on the first node you did.
Now, still on your "background copy" + mask layer, right click with your pen tool and select "Make Selection" with a feather of 0 pixels. Click "Ok" and the selection should appear around the part you wanted extracted. Like this.
Next step is to extract. Do Select > Inverse and the selection should now be around the outside of Robin.
Next, do Edit > Fill > Foreground Color (which should still be black). Make sure you're still on the mask layer! It should now look like this:
You can do Select > Deselect to take the selection off now.
If you notice some marks that haven't been extracted proporly, just use the pen tool, and go through the extraction process again.
Note: when you close the path, right click and select "make selection" but don't do the selection inverse for this part. Just do Edit > Fill > Foreground color, because you don't want to extract the background anymore, you want to take off the parts that weren't extracted proporly. Like:
When you close your path (like in the image above) just right click, and select "Make Selection" and then Edit > Fill > Foreground color. Got it?
On to the last page!