_modal.slim

<div class="modal fade" id="modal" tabindex="-1" role="dialog" aria-labelledby="modalLabel" aria-hidden="true">
  <div class="modal-dialog modal-dialog-centered" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="modalLabel">New message</h5>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">&times;</span>
        </button>
      </div>
      <div class="modal-body">
	      <img src="" class="imageurl" style="width: 400px; height: 264px;" >
      </div>
    </div>
  </div>
</div>

javascript:
	$('#modal').on('show.bs.modal', function (event) {
	  var button = $(event.relatedTarget) // Button that triggered the modal
	  var imageurl = button.data('imageurl') // Extract info from data-* attributes
	  var modal = $(this)
	  var img = modal.find('.imageurl')
	  img.attr('src', imageurl)
	})