Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a861e9f1dbbc25c92471956a6e3a0d21.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563