Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/dd19fdc181b8839b6c3e904b2b3bc5d4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563