"Ignore atmosphere settings" is a checkbox in the "Camera backdrop options" (where you load the photo).

I don't think the atmosphere is the problem if you are seeing "stripes". Sounds more like a scaling issue. Can you post a sample render and the original cloud image? Based on that I might be able to tell what is happening.

 

Here is an example using this technique. The sky is an old photo (not the greatest quality and resolution).

 

Ciao

TD