How to display Blogger first image in a post?

The xml snippet below will call the first image in a blogger post.

<b:if cond='data:post.firstImageUrl'>
 <img expr:src ="data:post.firstImageUrl" expr:alt="data:post.title"/>
 </b:if>

But the problem is that it only shows when the image is published along side with the post. Is there a code to grab the first uploaded image? Please answer in the comment.