Large-scale visual effect - - not working

Here is a screenshot of a photo that I removed the sky from in photoshop. I placed this image on a plane in blender, and I want the sky to be rendered ‘as aplha’ if that is correct term. How is this possible?

After experimenting, I think I may be asking the wrong question.
I want to have huge wave or other object approaching the camera from behind the buildings.

The highlighted vertical plane is the one with the image of the buildings, and I figured out how to make only the sky alpha. But the problem is, the wave is still not visible, because alpha causes the world/background to show through. How can I fix this without making a complicated mesh to fit the buildings exactly??


Have you enabled ZTransp in F5? Without it the alpha shows the sky colour.

I did it and it worked. Thanks a lot! ! I never knew what that button did!:smiley: