images will be black opacity

/* images will be black opacity*/  just use this css & call grayscale as a class
.grayscale:hover {

  /* for Webkit browsere, Chrome 19+, Safari 6+ ... */
  -webkit-filter: grayscale(1);

  /* this is for Firefox 3.5+, Firefox mobile */
  filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'gs\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#gs");

  /* for IE6+ */
  filter: gray;
}