Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/4ff3742b7f29e83d25b3b2df9ceb6307.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563