No, the captcha code is not intended by default to be case sensitive. This can be modified however by modifying the Server Validation that performs the captcha validation.
The code will look similar to:
$WAFV_Errors .= WAValidateLE((strtolower(isset($_POST["Log_in_group_Security_code"])?$_POST["Log_in_group_Security_code"]:"")) . "",((isset($_SESSION["captcha_Log_in_group_Security_code"]))?strtolower($_SESSION["captcha_Log_in_group_Security_code"]):"") . "",true,3);
to make it case sensitive, remove the strtolower functions:
$WAFV_Errors .= WAValidateLE((isset($_POST["Log_in_group_Security_code"])?$_POST["Log_in_group_Security_code"]:"") . "",((isset($_SESSION["captcha_Log_in_group_Security_code"]))?$_SESSION["captcha_Log_in_group_Security_code"]:"") . "",true,3);