CSS3 Grayscale filter Property

style.css

// filter: 
// none | blur(px) | brightness(%) | contrast(%) | drop-shadow(h-shadow v-shadow blur spread color) |
// grayscale(%) | hue-rotate(deg) | invert(%) | opacity(%) | saturate(%) | sepia(%)	 | url(); 
// initial inerit

.class .class img {
    -webkit-filter: grayscale(100%);
    filter: grayscale(100%);
}

.class img:hover {
    -webkit-filter: none;
    filter: none;
}