How do I reference an image from text/description field? In some cases, I am entering some text and an img src tag in descriptions and text fields on my content pages rather than use an image field, for example the Header field on a view. 

I cannot work out the location to use. I thought images/imagefilename.jpg would do the job, but alas no. I also want to avoid the old http://hostname.com/images/imagefilename.jpg for vairous reasons. 

My images are in themes/mytheme/images.
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;