Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a2fd3ba6ee9e2a75c6ed9f2f421538e0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563