Hello,
If captcha not work properly it is the problem of Captcha Plugin. If you don’t want to show Captcha in login form go to sb-login/template/login-form.php
Find this line and remove it
<p><?php if( function_exists( 'cptch_display_captcha_custom' ) ) { echo "<input type='hidden' name='cntctfrm_contact_action' value='true' />"; echo cptch_display_captcha_custom(); } ?></p>