If you are using 'captcha' , you must also include
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/captchaimage.aspx"))
to allow the image to appear
and probably best also:
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/passwordrecovery.aspx"))
EDIT:
recommend: //it's not login/logout page
if ((!CommonHelper.GetThisPageURL(false).ToLower().Contains("/login.aspx"))
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/register.aspx"))
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/contactus.aspx"))
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/captchaimage.aspx"))
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/passwordrecovery.aspx"))
&& (!CommonHelper.GetThisPageURL(false).ToLower().Contains("/logout.aspx")))