The only problem with this is that not all browsers support it, like Internet Explorer 6,7,8 and Opera. Mozilla Firefox, Google Chrome and Safari as far as I know supports the drop shadow effect.
How to add Drop Shadow effect?
To do this first log in to your account -> Layout -> Edit HTML -> Under the Edit Template Box, Find .post img this class refers to all images in all your post.
Next is to add this code:
-moz-box-shadow: #222 4px 4px 10px; /*For Mozilla Firefox*/
-webkit-box-shadow: #222 4px 4px 10px; /*For Safari and Chrome*/
-webkit-box-shadow: #222 4px 4px 10px; /*For Safari and Chrome*/
Then click Save Template and your done. You can change the padding and the color of the shadow as you want.