Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3c4d987e2a0d142c6cf2df888ceb9d99.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563