I found this question on Quora.
Here’s my answer:
- Select the hair including a little area around it using a lasso.
- Make that a layer.
- Use the grass-shaped brush to erase the extra parts of the layer including small parts of the hair.
Ultimately, you won’t get the hair exactly as in the original, but it will look like well-blended hair. You may need to fiddle with the opacity of the eraser in order to get just the effect you’re looking for.
I used that technique for this. I probably could have gotten a better effect if I’d gone over it again with a lower opacity.