How to make image/camera effects like in "Bluk"?

Hey guys. I just stumbled across this Game called “Bluk” and I am really curious of how the author achieved the front layer image effect thats shown as some kind of gradient/fog at the bottom of the screen. Do you have any ideas what technique he was using?

Thanks in regards

Screen:
89770-bluk.jpg

That looks simply like a semitransparent gradient on an image overlay to me.