I'm not sure I understand the question. You can't do anything with background objects. Nope, nothing. That's why they don't use up processing power. You either have to move the screen to act with the background or if you want moving backgrounds, you have to make them active (picture) objects.
Disclaimer: Any sarcasm in my posts will not be mentioned as that would ruin the purpose. It is assumed that the reader is intelligent enough to tell the difference between what is sarcasm and what is not.