if you remove the captcha image, you need to also remove the captcha validation:
$WAFV_Errors .= WAValidateLE((strtolower(isset($_POST["Security_Code"])?$_POST["Security_Code"]:"")) . "",((isset($_SESSION["captcha_Security_Code"]))?strtolower($_SESSION["captcha_Security_Code"]):"") . "",true,5);
delete that line.
if you look at the code to create the captcha image:
<div class="fieldGroup"><img id="capt1" src="webassist/captcha/wavt_captchasecurityimages.php?width=220&height=50&field=Security_Code_1&bgcolor=CCFF00&transparent=0&bgimage=&gridfreq=20&gridcolor=000000&gridorder=behind&noisefreq=20&noisecolor=000000&noiseorder=behind&characters=6&charheight=&font=fonts/MOM_T___.TTF&textcolor=000000" alt="security code" width="220" height="50" /><img src="webassist/captcha/images/refresh.png" height="18" onclick="document.getElementById('capt1').src+='&ref=1'" /></div>
Look for the "field" querystring variable being passed:
&field=Security_Code_1&
the captcha session variable will use the value of the field querystring variable with "captcha_" in front as the name:
captcha_<fieldQuesrystring>
or in this case:
captcha_Security_Code_1