img[src*=captcha]{
    filter:url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><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 0.1111 0 0 0 1 0\'/></filter></svg>#grayscale"); /* Firefox 10+ */
    filter:gray; /* IE6-9 */
    -webkit-filter:grayscale(100%); /* Chrome 19+ & Safari 6+ */
    -webkit-transition:all .6s ease; /* Fade to color for Chrome and Safari */
    -webkit-backface-visibility:hidden; /* Fix for transition flickering */
}