Loading Image progress

Sometimes, in my projects, I needed to display progress of the image loading. It is not a big deal to display some animation stuff or some text during the image loading. But what if we need to display real progress of the loading, I mean percentage? After doing some research in internet, I found unusual solution to this problem. I think it is kind of trick where you can add ProgressBar as a child to Image. Another words, extend Image class adding ProgressBar which will display progress of its own loading.
This solution I found on Tony Fendall's blog and please check it out with source code.