[Zope] how to get the value of image properties?

[Joonas Rapila]

I think I saw an example of this at the zope site, but couldn't find 
it anymore..
The problem:

I need the "width" and "height" -values of images as dtml-strings, 
but how is it done?

an example:

<TD WIDTH="[the width of image1]"><dtml-var image1></TD>
            ^^^^^^^^^^^^^^^^^^^^^
            How do I get this? (for example, it could be something like "100")