Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/7a8cc8cc3e0d2bd8b95e2d6e81ddf172.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563