the code to show the captcha image will look something like:
<img src="webassist/captcha/wavt_captchasecurityimages.php?width=200&height=50&field=Security_Code_1&bgcolor=FFFFFF&transparent=0&bgimage=&gridfreq=20&gridcolor=000000&gridorder=behind&noisefreq=20&noisecolor=000000&noiseorder=behind&characters=5&charheight=&font=fonts/MOM_T___.TTF&textcolor=000000" alt="security code" width="200" height="50" />
edit that, so that it has an id:
<img id="capt1" src="webassist/captcha/wavt_captchasecurityimages.php?width=200&height=50&field=Security_Code_1&bgcolor=FFFFFF&transparent=0&bgimage=&gridfreq=20&gridcolor=000000&gridorder=behind&noisefreq=20&noisecolor=000000&noiseorder=behind&characters=5&charheight=&font=fonts/MOM_T___.TTF&textcolor=000000" alt="security code" width="200" height="50" />
then add a refresh image next to it with an onClik event to regenerate the captcha graphic:
<img src="refresh.png" height="18" onclick="document.getElementById('capt1').src+='&ref=1'" />