Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b1b3522c6eb1017c96e95f1c8e52f537.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563