Hello,
The following markup is being used to generate the image on your Front page:
<img class="alignnone wp-image-146" alt="Kanga for Hire" src="http://bigzhire.files.wordpress.com/2013/06/bzlr1.jpg?w=990&h=480" width="990" height="480">
To fix the image so that it is responsive (and aligns at all browser widths), add a class of “size-full” to the image. Here is an example of this:
<img class="alignnone size-full wp-image-146" alt="Kanga for Hire" src="http://bigzhire.files.wordpress.com/2013/06/bzlr1.jpg?w=990&h=480" width="990" height="480">
Please let us know how this works for you.