Originally Posted by MasterZap

If you want to put the sky bitmap in the haze slot, read this. You need to turn it's output up to around 10-ish.

If you just want to use it as an actual background image, well, then just use it as a normal spherical environment in the environment map (remove the physical sky completely), or, if you only want it as a background image, use it in the "background" slot of the physical sky itself. Either way, you should also read this to understand that you need to turn it's output level up approximately 2500,0

/Z