css url() not recognized in internet explorer 10

The content property is only valid on :before and :after pseudo-elements. You should change it to:

.ui-icon-zoom-in { 
  background: url(images/16x16/ZoomIn.png) no-repeat; 
  width:16px;
  height:16px;
}

Apart from that, IE8+ only supports content property if a valid DOCTYPE is specified.

The content property is only accepted on :before and :after pseudo-elements in CSS3. You should probably use a jQuery selector to append the image to the object:

$("#zoomin").html("<img src='images/16x16/ZoomIn.png' alt='Zoom In'>");