<span class="frame"><img src="http://seangaffney.cc/new/img/me.jpg" /></span>

<span class="frame"><img src="http://a3.twimg.com/profile_images/1136130947/twitter-dribbble-profile-pic_reasonably_small.png" /></span>

<span class="frame"><img src="http://a3.twimg.com/profile_images/1100546975/Screen_shot_2010-08-11_at_9.08.03_AM_reasonably_small.png" /></span>


<span class="frame"><img src="http://a2.twimg.com/profile_images/935982818/avatar_main_copy_square_reasonably_small.jpg" /></span>

body{background:#333; padding:10em;}

.frame{
    display:inline-block;
    position:relative;
    overflow:hidden;
}
.frame>img{
    vertical-align:top;
}
.frame, .frame:before{
    -moz-border-radius:100em;
    border-radius:100em;
    
}
.frame>img{
    -webkit-border-radius:100em;  
}
.frame:before{
    content:'';
    display:block;
    position:absolute;
    left:0;
    right:0;
    width:100%;
    height:100%;
    margin:-10em;
    border:10em solid #333;
}