I'm sure someone else knows, but I think the bmz functons automatically kick in when an image is requested from the cart-side page display. But also you can call up individual product images with the handler admin, and play around.

You can always clear the cache (specially if you use my mod above!) and see how it gets filled up after a cart-side page request.

Presumably if you change an image size setting, the old images named .image.(width)x (height) will be left in the cache folders, new ones of appropriate size will generate on the next page request.

So each cached image has its size as part of the long filename, so different sized images are created to suit, and are unique to a particular size.

If you want to know if the page is using cached images, look at the picture url, if its cached, it has 'bmz_cache' in the image 'src' url, as it comes from that cache folder.

Incidentally I think I've found a way of running the cache outside of web space, anyone interested, do p.m me. But it needs code changes.