Thanks guys. So i'm guessing the options are:
1) Create custom code
2) Have a CTA button drawn into the image but make the whole image clickable (not sure I like this as the button won't do the whole change shade thing when hovered over)
<img border="0" src="http://www.faradaykeynes.co.uk/images/accountants_miltonkeynes.png" width="" height=""></p>
<div style="position: absolute; width: 72px; height: 88px; z-index: 1; left: 253px; top: 131px" id="layer1">
<a target="_blank" href="http://www.faradaykeynes.co.uk/index.php/aboutus">
<img border="0" src="http://www.faradaykeynes.co.uk/images/FK-images/about-us.jpg" width="108" height="86"></a></div>
Kevin,
You are in danger of over thinking this. Putting the CTA on top of an image is popular but the general UX is poor. A CTA button should stand out - plonking it on an image might look great on your computer but it might well look naff for someone using a small screen.