Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/17f7b9d84eb526d6aaf2506f50e8f293.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563