Session for Wordpress plugin

session.php

// session value
function keksus_ae_session(){
	global $option_name,$options;
	if( $options['captcha_on'] == '1' ){
		session_start();
		if(headers_sent()){
			$digits = $options['captcha_digits'];
			$_SESSION['captcha'] = rand(pow(10, $digits-1), pow(10, $digits)-1);
			$captcha  = $_SESSION['captcha'];
			return $captcha;
		}
	}
	elseif(isset($_SESSION)){
		session_destroy();
	}
}
add_action('init', 'keksus_ae_session');