标记:
<div class="post">
<div class="thumbnail">
<img class="thumb" src="http://placehold.it/950x450/" />
</div>
</div>
CSS:
.post {
width: 500px;
}
.post img.thumb {
width: 100%; /* fill available space of parent and keep aspect ratio */
}
小提琴:
http://jsfiddle.net/