<div class="comment">
     ... user content here, including <img>'s
</div>

.comment img {
    display: block;
    max-width: 512px;
    -webkit-transition: 350ms ease all;
       -moz-transition: 350ms ease all;
        -ms-transition: 350ms ease all;
         -o-transition: 350ms ease all;
            transition: 350ms ease all;
    margin: 20px auto;
    border: 2px solid #777;
    -webkit-box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
       -moz-box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
            box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
    -webkit-filter: blur(20px);

}

.comment img:hover {
    -webkit-filter: blur(0px);
}