You should make the container relative and give it a height as well and you’re done.
http://jsfiddle.net/jaap/wjw83/4/
.main {
width: 300px;
margin: 0 auto;
overflow: hidden;
position: relative;
height: 200px;
}
img.absolute {
left: 50%;
margin-left: -200px;
position: absolute;
}<div class="main">
<img class="absolute" src="http://via.placeholder.com/400x200/A44/EED?text=Hello" alt="" />
</div>
<br />
<img src="http://via.placeholder.com/400x200/A44/EED?text=Hello" alt="" />If you want to you can also center the image vertically by adding a negative margin and top position: http://jsfiddle.net/jaap/wjw83/5/