You can do it with pseudo-elements: (demo on dabblet.com)
your markup:
<div class="parent">
<div class="child"> Hello I am child </div>
</div>
css:
.parent{
position: relative;
}
.parent:before {
z-index: -1;
content: '';
position: absolute;
opacity: 0.2;
width: 400px;
height: 200px;
background: url('http://img42.imageshack.us/img42/1893/96c75664f7e94f9198ad113.png') no-repeat 0 0;
}
.child{
Color:black;
}