Açıklamama gerek yok heralde gayet açıklayıcı :)

CSS KODU:

a.linkopacity img{
filter:alpha(opacity=50); -moz-opacity: 0.5; opacity: 0.5;
}
a.linkopacity:hover img{
filter:alpha(opacity=100); -moz-opacity: 1.0; opacity: 1.0;
}

HTML KODU:
açıklama