A solution to this would be to create an empty IMAQ buffer (with IMAQ Create) that was the size of two of your pictures placed together (or the size of the non-overlapping portions of two pictures placed next to each other). Then, using IMAQ Overlay Bitmap.vi, you could overlay the pictures to the correct area of the image buffer and then using IMAQ Merge Overlay, you would merge the overlays onto the image buffer.
If you wanted to do the matching up of pictures programatically, you could implement an algorithm using IMAQ Pattern Match to determine what part is overlapping and extract the non-overlapping section.
Hopefully this gives you some ideas. Good luck with your project!