That login module on our demo website is the standard joomla login module.
The image on the header of the module on the demo website was added with CSS.
However, the CSS to use will depend on the way your template handles the display of the module header, so I can't tell you exactly what CSS to add without looking at the CSS on your website.
On our demo website, we use that CSS for example :
.moduletable-cart h3 {
padding-left: 15px;
padding-top: 5px;
color: white;
font-size: 12px;
background: url(../images/cart_top.png) no-repeat;
height: 25px;
}