Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f5a0e2966176e5dfd4a6243c1f2cb8ff.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563