Using :before CSS pseudo element to add image to modal

http://caniuse.com/#search=::after

::after and ::before with content are better to use as they’re supported in every major browser other than Internet Explorer at least 5 versions back. Internet Explorer has complete support in version 9+ and partial support in version 8.

Is this what you’re looking for?

.Modal::after{
  content:url("https://stackoverflow.com/questions/6668577/blackCarrot.png"); /* with class ModalCarrot ??*/
  position:relative; /*or absolute*/
  z-index:100000; /*a number that's more than the modal box*/
  left:-50px;
  top:10px;
}

.ModalCarrot{
   position:absolute;
   left:50%;
   margin-left:-8px;
   top:-16px;
}

If not, can you explain a little better?

or you could use jQuery, like Joshua said:

$(".Modal").before("<img src="https://stackoverflow.com/questions/6668577/blackCarrot.png" class="ModalCarrot" />");