If I am following your idea correctly a div can solve that.
Where you have the logo defined as
<img src="http://test.example.com/rs/test/images/logo.gif" align="right" border="0" height="39" width="90" alt="" />
you define a new div and set its ID distinct from existing ones
<div class="mktEditable" id=replace_logo>logo<br />
<img src="http://test.example.com/rs/test/images/logo.gif" align="right" border="0" height="39" width="90" alt="" />
</div>
The results is an editable image: