Inspired by the GIMP Luminosity Mask tutorial made by Pat David, I have made by a template using a photograph made by the (U.S.) National Park Service at Western Arctic National Parklands. It is 100% nondestructive approach, so you can go ahead and use your image and go straight away to dynamically edit.

Image Link - https://www.flickr.com/photos/nps_wear/8517263428/

Tutorial Link - https://www.gimp.org/tutorials/Luminosity_Masks/