Even i have found such missing entries in some of the templates i have used.
The reasons for missing file in a normally working template can be a result of development process. – May be designers used the pic during development, made entry to the css file and later did not use it.
One should remove such “NOT FOUND” entries, as it results in poor performance of Joomla.
<blockquote>General:
Watch out for errors in your template. When you reference a file like arrow.gif and this file is non-existent, the performance of your server will drop immensly.</blockquote>
the above quote is from the Joomla.org forum thread http://forum.joomla.org/viewtopic.php?t=50278
If your template is working normally without that image and you do not find any layout problems, you can remove the entry of the image.
Example : If i have a image file “bullet.gif” , which is not found in web stats (as you say) and i want to remove the entry. Then this is what i do
Search your css files for similar entry :
background: url(../images/bullet.gif) no-repeat ;
Make it look this way :
background: none ;
I would advise NOT to remove the whole block from the css file. Experiment only after taking backup of original file.