How to give outer glow to an object in a transparent png using CSS3?

This can be done using filter(drop-shadow).

Here is a demo http://jsfiddle.net/jaq316/EKNtM/

And here is the code

    <style>
        .shadowfilter {
        -webkit-filter: drop-shadow(12px 12px 7px rgba(0, 0, 0, 0.5));
         filter: drop-shadow(12px 12px 7px rgba(0, 0, 0, 0.5));
    }

    .bottleimage {
        width: 500px;
    }
    </style>
    <img 
        src="http://upload.wikimedia.org/wikipedia/commons/c/ce/Coca_Cola_Zero_bottle.png" 
        class="shadowfilter bottleimage"/>