Take a look on or around line 767 in your style.css file and remove or change the padding to 0. The reason its doing that is due to the padding that is added when a content image is hovered over. Removing the padding fixes it.
#content a:hover img {
-moz-transition:all .5s ease;
-o-transition:all .5s ease;
-webkit-transition:all .5s ease;
transition:all .5s ease;
opacity: .5;
padding: 0;
}
Let me know if that works
