image hover;

<style type="text/css">
    .nizzle {
    position: absolute;
    overflow: hidden;
    opacity: 0.9;
    bottom: 1px;
    left: 1px;
    background-color: transparent;
    }

    .shizzle {
    position: absolute;
    overflow: hidden;
    opacity: 0.0;
    bottom: 1px;
    left: 1px;
    -webkit-transition: all 0.9s ease-out; -moz-transition: all 0.9s ease-out;
    }

    .shizzle:hover {
    opacity: 1;
    -webkit-transition: all 0.9s ease-out; -moz-transition: all 0.9s ease-out;
    -webkit-filter: grayscale(0)
    }

</style>

    <div class="nizzle">
    <img src="URL">
    </div>

    <div class="shizzle">
    <img src="URL">
    </div>