You've got other issues you need to work out as well, but just give that IMG a unique class (since you may eventually have other images that need to be responsive) and then write styles for it. I did the following:
Line 127 (below the current CSS):
table[class="body"] img.img-responsive {
width: 100% !important; height: auto !important;
}
and:
<img src="http://info.the451group.com/rs/the451group/images/ejournal_image_580x195.jpg" alt="banner" class="img-responsive" />