[fatsheep]

Thanks for the instructions. I went out and took some pics and I'm trying this but I ran into a few roadblocks:

Originally Posted by Mr. Pickles

Try this.....should work in GIMP, PS, etc...
- Adjust curves on dark image to set levels

I know where the curves tool is but I'm not sure how to use it effectively. The help manual wasn't too much help either... I just messed around with it until I found a setting that looked good.

Create a layer mask on Dark layer, copy monochrome dark stock image, paste in to layer mask and anchor

So I am pasting the desaturated dark image into the layer mask for the dark layer? This would mean I would have the desaturated dark image for both the layer and the layer mask.