Serving images via iRules from v11.1

Thanks to everyone who answered here.

The problem has been resolved. Uni's suggestion of looking at the logs proved to be key. I guess I should have realized that they would be in /var/log/ltm. Turns out the problem was due to my not removing (or modifying) a pre-existing redirection iRule that I had attached to the virtual server. It's a little counterintuitive (for me), but what was happening is since I stacked the Maintenance page iRule in front of the existing redirection, the maintenance page code was invoked when all pool members were down - this is why under some circumstances I could see the image sort of "fly by". then the next iRule attempted to redirect to URIs that weren't working (because there were no active pool members), which messed things up. After removing the redirection iRule, the maintenance page comes up. How stupid of me. Thank you, Uni, for pointing me to the log location. Thank you everyone, for answering so promptly!