I know it isn't difficult, but it has been somewhat of a challenge for me (probably because I initially learned computer graphics from a simple, Windows-based painting program). This first image was originally two different images from two different areas in the sky (albeit at about the same time and sun direction). the vehicles were not this close together - or at least not when I finally captured the two images. Their exposures were not quite the same for some reason so I had to tweak the brightness of one of them (I chose to lighten the image with the fixed wing in it), and you may be able to sense that in the image. But I learned a lot in the process. Had the two images not been on the same background it could have been more difficult, but because the background was the same expected subject (sky) it was slightly easier. The image below was also two separate images and had to be blended because the focus was different in each of the two images. Frog on the right was focused in one image and frog on the left was focused in another. I wanted them both to be in focus, so I layered and blended the two. the difficulty here was that the two images were not composed similarly - they were close but no cigar. So some jockeying had to be done before the two target subject didn't overlap (which would have ruined the effect). With both of these the secret of course with layers is - black to reveal, white to conceal (I get these backwards all the time - there should be an acronym to remember it). Once you get the layers adjusted geometrically where and how you want them, you create a mask layer and paint away (to reveal the bottom layer through the top layer - at least that is how I did it). I'm sure that some of my methods (not all described here were somewhat unconventional, but it got the job done and as I mentioned earlier, I really learned a lot this weekend. I feel like such an infant with this stuff!