Add Images in WebForm Dropdown list
It would probably be better to have that form coded by hand where you can turn your  list into a set of divs with a jQuery library, eg. http://designwithpc.com/Plugins/ddSlick

Or, you can set a background image to each option with CSS (which kinds of takes a bit of time depending on how much options you have in your select list):

select option[value="your_value"] {
  background-image: url(your_image.png);
}