I had someone ask me how to do this, this morning so I thought I'd post it. You can do this with GIMP, Photoshop or many other programs as well, but here's Bob Elliots. favorite and it's pretty easy. If you know of an easier way, let me know. I just downloaded the program and used it for the first time. Download Photoscape free at http://www.photoscape.org/ps/main/download.php

First Crop the Infrared Pic
1. Click Editor at the top.
2. Find your overlay photo (infrared) and click on it.
3. Click on crop and crop this photo how you want it.
4. Click save to save it.

Now for the overlay
1. Click Editor at the top (probably already there).
2. Find your base photo and click on it.
3. On the bottom, click on the Object Tab.
4. Click the Photo button (little picture of mountains and a sun)
5. Click Photo.
6. Browse and select the photo you're overlaying. Lower it's opacity (aka transparency) to a value you like. This allows you to see through to the bottom image.
7. Move the image to the spot you want it at.
8. Click Photo + Objects, click Ok.
9. Click Save.

Once you do it once or twice you'll find it pretty simple.

Glad you go it working well. Works good for making custom headers on websites too