$(document).ready(function(){
$("#btn_admin").hover(function() {
        $(this).attr("src", $(this).attr("src").split(".").join("_over."));  // adds _over to the name of the image
  }, function() {
        $(this).stop(true,false); // prevents the creation of stacked actions
        $(this).attr("src", $(this).attr("src").split("_over.").join("."));  // removes _over from the name of the image
        $(this).attr("src", $(this).attr("src").split("_down.").join("."));  // removes _down from then name of the image, if clicked before
  });
$("#btn_admin").mousedown(function() {
        $(this).attr("src", $(this).attr("src").split("_over.").join("_down."));  // adds _over to the name of the image
  });
});