I've hunted all around, and I find conflicting information.
What I'm looking for is to have an icon appear when inserting a non-image into a WP page. Right now all I get is a link.
In the ADMIN section, under media library an icon does appear, but not on the site's pages.
Seems at one time you could put special named files in the theme/images directory and get them to show, then later it was hard coded to the "crystal" icon set.
I did find a plug in that supposed allow you to link images to non-image media called "Custom Thumbnails" but it doesn't work very well, and I wanted to get the functionality back that apparently *used* to exist in wordpress but for some reason is now gone...
I read somewhere among the various technical sites that the function was "gutted" and hard coded to the crystal icon set somewhere around ver 2.5 (??)