overflow:auto). Hence I needed to add the listener to this DIV, and compute coordinates for the image taking the DIV into account. Like most things, easy once you know how (translation, after numerous failed attempts, and the occasional "doh!" it seems to work).
You can see lazy loading in action if you view a BHL item, such as Item 26140. Note that this implementation of lazy loading doesn't work in Safari, much to my chagrin (it's my default browser). It works fine in Firefox