用CSS实现的透明效果

兼容各种主流浏览器

img {
    opacity: .75; /* Standard: FF > 1.5, Opera, Safari */
    filter: alpha(opacity=75); /* IE < 8 */
    -ms-filter: "alpha(opacity=75)"; /* IE 8 */
    -khtml-opacity: .75; /* Safari 1.x */
    -moz-opacity: .75; /* FF < 1.5, Netscape */
}