Using custom fields to select head image

Hi All,

I am trying to use a custom field in a page (not a post) to select which image to use for the header of each page.
My idea is to call the field name “zone” and then use an if statement to select the value eg. “nt” or “sa” or “general”

I have no idea how to do this and everything I have tried so far causes errors.

Any ideas?

Thanks in advance.

Ryan