Was bored and thinking of something to try out in Gimp, a fake thermal image seemed a easy enough try, so I created a gradient (which you can download at the end of this post) and set about colouring an image in depth map style but using black as coldest and white as the hottest parts of the image. I then mapped to my new gradient and gave the image a slight blur.

I'll admit the image is all a bit rushed but just wanted to get something done to show you the potential of this gradient.

Below is my image from Original to Greyscale to Gradient Mapped.

How does it actually work? Do pictures have heat signatures?

Anyhow neat job

Lovely effect he4rty!

Erisan - Thanks for the comment
Sallyanne - Nice results, the greyscale image I created in the first post wasn't done using any filters or scripts but by selecting different parts of the image and filling with various greyscale gradients by using the blend tool and the shaped fill patterns. You could also use the paintbrush tool and paint the image from black to white to manually identify your own heat signatures.