img {
    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 0 0 0 1 0'/></filter></svg>#grayscale"); /* Firefox 3.5+ */
filter: gray; /* IE6-9 */
-webkit-filter: grayscale(1);
-webkit-transition: all 0.5s ease-in-out;
-moz-transition: all 0.5s ease-in-out;
-o-transition: all 0.5s ease-in-out;
-ms-transition: all 0.5s ease-in-out;
transition: all 0.5s ease-in-out;
}

img:hover{
filter: none;
-webkit-filter: grayscale(0);
-webkit-transition: all 0.7s ease-in-out;
-moz-transition: all 0.7s ease-in-out;
-o-transition: all 0.7s ease-in-out;