O.k, first....
1. With your main picture of the moon use the rectangular marquee tool and select a sqare that includes the moon and some area around it (above below side to side). Copy and paste this and put it behind the main moon picture (in the layer selection).
(Note photoshop should probably have pasted it in the exact same place it was copied from so you shouldnt need to move it.
2. On your main moon picture use the "magic wand" tool , (with a tollerance setting at prob like 15 or so) and select the moon while holding down the "shift" key so that you can select all of it, once you have done this press "delete" on your keyboard.
(Note your picture should look no different because of the piece we copied and pasted from step one).
3. Now, you are going to need to save two layers. Make it so that you can only see the moon pic in the background that we copied and pasted. (to turn off layers click on the eye beside the layer you want to turn off, same thing to turn it back on)
Save it as background.png or something. Has to be .png though, not jpeg or something.
4 Now save you're main moon pic. (turn on the main moon layer and turn off the copied and pasted pic layer). Save as moonoverlay.png or something like that.
5. Now in UXArchitect place the background.png down first, then put down the icon over top of the moon so that it covers all the moon.
6. Now insert moonoverlay.png over top of that, the icon will now appear in the moon when something is selected, and if there is no icon , all you will see is the moon.
Here's some pics:
