Adding an image to your RSS 2.0 feed is known to be perfectly harmless, and can add some color and jazz to your feeds in the feed-readers’ display. Of course, the effect is entirely cosmetic, but heck, if you can spend hours modifying the design of your blog, why not spend a few minutes modifying how your feed is displayed in readers, considering the fact that a lot of your regular readers might be using a feed reader?
To add an image to the RSS 2.0 feed created by your WordPress weblog, create an image (the maximum value for the width and height for RSS 2.0 feeds are 144 and 400 respectively), upload it to your wp-content folder, which is intended to hold all user-content, and edit your wp-rss2.php file/template to include the image. Change the permissions of the wp-rss2.php file to 666, and you can use WordPress’ in-built template editor to do the editing.
Here is the relevant portion from WordLog’s RSS 2.0 feed :
<title><?php bloginfo_rss('name') ?></title>
<link><?php bloginfo_rss('url') ?></link>
<description><?php bloginfo_rss("description") ?></description>
<copyright>Copyright <?php echo mysql2date('Y', get_lastpostdate()); ?></copyright>