Correct way to use Image Thumbnails in HTML widget?

CM1 conveniently creates a thumbnail version of the images that we upload but is there a correct way to use them in an HTML widget?

In the HTML, if I add thumb_ before the filename like this:

/Assets/myawesomewebsite/images/ **thumb\_** myimage.jpg

The pages look great when published, however they appear as broken images in the CM1 preview.

Just an update on this - the thumb_* images are intended to be used by the Rich Text widget.

We will make this post an Idea.  If any users would also like to use the thumb_* images in HTML widgets please let us know!