jQuery Link Ativo
by Tiago Sousa
HTML
<button id="my_btn"><img src="http://placekitten.com.s3.amazonaws.com/homepage-samples/200/140.jpg" /></button>
CSS
.ativo > img{
opacity: 0.5;
}
JavaScript
$('#my_btn').click(function() {
$(this).toggleClass('ativo');
});