How do I reference an image from text/description field?
Unless the location of your Drupal install changes (sub directory versus root directory), the easiest way would be to use a relative path from the site root to the image.

&lt;img src="/sites/all/themes/mytheme/images/imagefilename.jpg" /&gt;


You could get the file path with a PHP snippet. Note that the PHP filter module needs to be enabled, and the PHP code text format selected, for this to work.

&lt;?php $path = base_path() . path_to_theme() . '/images'; ?&gt;
&lt;img src="&lt;?php print $path; ?&gt;/imagefilename.jpg" /&gt;