.wp-caption, .wp-post-image, .thumbnail { position: relative; }
.wp-post-image:hover .wp-image-credit { opacity: 1.0; }
.wp-image-credit { opacity: 0.4; text-shadow: 0 1px 1px #444; display: block; width: auto; padding: .6em; position: absolute; bottom: 0; left: 0; font-size: 0.9em; color: #fff; text-shadow: 0 1px 1px #000; text-align:left; padding-left: 10px; }
.wp-image-credit:hover { opacity: 0.8; background: rgba(0,0,0,0.6); }