Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3e91bb10a5c7e2c4dc570b2a397068d8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563