Harry's Mist and Fog

A script-fu to add to a photo a realistic effect of mist and fog. After treatment, you can delete excess mist by painting with a dark color and a soft brush on the layer's masks, or by adjusting the opacity of "Mist" and "Clouds" layers. You'll find this script in "Script-Fu/Effects/Harry's mist".
Comments are welcome, and I will consider any changes that you request.