Removing the border style for dynamically created asp image controls

Hello
sometimes we need to use the asp image control so we can generate  empty alt tags (visual studio 2005 does not render any attributes set to an empty string).  I know how to do this and also how to remove the border style that is automatically added (http://blog.josh420.com/archives/2007/10/aspnet-image-control-border-width-inline-style.aspx).  We implemented this 6 months ago, however, only today have I discovered that it does not work when images are created dynamically.
 
The first implementation was for asp images that have been set up within an aspx page:-
<asp:image runat="server" id="imgMast1" GenerateEmptyAlternateText="True" alternatetext="" imageurl="" />
The above works-no border style is rendered and the imageurl is populated in code.
I ha ...