How to Mask Flyaway Hair Using GIMP

Insert Background

1. 
   Insert a new background into the image. You might have one in mind or just experiment with something.

   1. You will see that your image has completely disappeared. Don't be concerned. It is just hidden.
2. 
   Move your new background to the bottom. If you can't, you probably need to anchor your floating selection.

   1. Process is being made but you can see some of the original background in the image. This indicates that some of the color adjustments weren't quite right from before.
3. 
   Select the layer Mask and then Color >> Levels.
4. 
   Start adjusting. What you want to do is get the hair strands even darker. The aim is to get the hair strands even darker (i.e. more transparent). So I move the left control to the center. You can see the results in the preview immediately.