[Zope] image border in Zope 2.7.x

[Chris]

Hi,

this is a rather trivial problem: I updated a Server from 2.6.2 to 2.7.4
I noticed that all images used within link tags are shown with a border if

<a href="#"><dtml-var my_image></a>

is used (yes, I know: use PT ... it's not my code) unless I set a style 
(border-width:0). 2.6.x did not show this border.

Is there a simple way to change Zope's way to render image-objects 
globally? I dont' want to change the dtml-code of other people's if 
possible.

Regards
Chris