How to display image instead of a value in Drupal 7?
I can suggest an idea I used in Views output — this may help you find a solution for your case. I needed to display an icon near an article depending on its material type. I added a hidden PHP field with the following code (image names are not directly the same as the type name, that was the brief :)):

&lt;?php
switch ($row-&gt;type) {
case 'article':
  print 'articles'; break;
case 'gallery':
  print 'gallery'; break;
case 'music':
  print 'music';
}
?&gt;


And then a “type” field, which had the following override:

&lt;img src="/sites/all/themes/my_theme/images/[php].png" alt="[type]" title="[type]" width="22" height="22" /&gt;


[php] is where Views output inserts the output of the PHP field I showed earlier. This same approach can be used to add a class to the HTML tag, and define a CSS image background for each class.

I hope this helps to find a solution for your problem.