Check out the WA_Globals.php file
in the WA_Globals directory....
$WAGLOBAL_Captcha_Width = "120" ;
$WAGLOBAL_Captcha_Height = "24" ;
$WAGLOBAL_Captcha_Characters = "5" ;
$WAGLOBAL_Captcha_Font = "Fonts/MOM_T___.TTF" ;
$WAGLOBAL_Captcha_BG = "cccccc" ;
$WAGLOBAL_Captcha_Noise = "000000" ;
$WAGLOBAL_Captcha_Text = "fffc00" ;
$WAGLOBAL_Captcha_BG_transparent = "0" ;