Content field list(text) : using correctly ?
I tried this too and it didn't work.  https://stackoverflow.com/questions/4248061/what-is-the-easiest-way-to-have-images-next-to-the-text-on-a-html-dropdown-combob you cannot put images in dropdown box in general (unless you use javascript).  I tried it as a 'Check boxes / radio buttons' widget and it did work.  Maybe that will be a good enough solution for you