colinjones: I'm not sure if that is possible, but I think the inverse is possible using area_detect:
# Detect motion in predefined areas (1 - 9). Areas are numbered like that: 1 2 3
# A script (on_area_detected) is started immediately when motion is 4 5 6
# detected in one of the given areas, but only once during an event. 7 8 9
# One or more areas can be specified with this option. (Default: not defined)
; area_detect value
I'm not sure if you'd do something like area_detect 1,2,3,4,6,7,8,9 to ignore the center of the image or if it would be multiple statements.
secs: Could you update the wiki or at least post what you did to get motion working so well for you? Do you have a problem with any of your cameras not updating? I've found it easiest to see this issue in a quad view. After a minute one or more of the camera images will stop refreshing. You can actually see the timestamp stuck at the time on the stuck ones while the working ones continue to change.
Bulek: When you say you upgrade motion, do you go through apt or get the newest sources and compile?