Thanks for the reply. It must have been a mod then because we definitely had it.
OK, so to protect our members' pictures I'm going to need to use permanent category based stamping then. I've turned this on in the categories and just changed to this ...
* Enable on-the-fly image protection
This option uses the watermark.php script to serve images - NO
I assume that's all I need to change. I'll see how that goes. We'll just need to be aware that we cannot ever retrieve any unstamped pictures.
The upside is that it's far more secure for people.