As you are modifying the classic template - see if there is a includes/templates/classic/common folder and if so inside this a tpl_header.php file. If not create the folder common there and copy the file at includes/templates/template_default/common/tpl_header.php to your pc.
Use notepad or a plain text editor and find the following and remove the red highlighted text and save. Upload FTP this to the folder you created
Code:
<!--bof-branding display-->
<div id="logoWrapper">
<div id="logo"><a href="http://moonandstarsgraphics.com/cart/"><img src="includes/templates/classic/images/ms_girlmoonsm.png" alt="Moon & Stars Graphics [home link]" title=" Moon & Stars Graphics [home link] " width="121" height="125" /></a></div>
<div id="taglineWrapper">
<div id="tagline"><h1></h1></div>
</div>
</div>
<br class="clearBoth" />
<!--eof-branding display-->
Which category image or on which page are you wanting a different size?