gistfile1.js

$('#feed').on("click", "img", function(e) {
  var offset_t = $(this).offset().top - $(window).scrollTop();
  var offset_l = $(this).offset().left - $(window).scrollLeft();

  var left = Math.round((e.clientX - offset_l));
  var top = Math.round((e.clientY - offset_t));
  
  //...