Background picture change on value

Unless I missed it, I would love to be able to have a "dynamic" background picture that would change based on a node value.

As one simple exemple, we would be able to change a background picture to show day or night environment while the front layer could display the weather condition. both would change based on their respective node value. 

Again, should it be possible and I missed it, disregard my post (but I would love to know how to program this ;-))

Regards,

Fabien