Hi:
You may need to change the STYLE template that you're using so that the USERTEXT style element has a justification of center. For ODS HTML, I do not believe that just= inside your style override will work for images.
There are some Tech Support notes that show how to change the UserText element. The method you use in your style template will differ, depending on whether you have SAS 9.2 or SAS 9.1.3.
cynthia