[Zope] automated setting of object properties?

I wonder if someone could offer advice on how to accomplish the following ... I notice that in version 2.x of Zope, uploaded images autmagically get their height and width properties set appropriately. This was not the case with version 1.x, at least for content import via the fsimport external method. I imported a slew of content with Zope 1.x and thus have a lot of images with height and width properties of 0. I would like to write an external method to scan through my entire database setting the height/width fields to their correct values. So far I haven't had any luck getting this to work. Any advice would be much appreciated. Cheers, Darran. -- Darran Edmundson [Darran.Edmundson@anu.edu.au]