Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/790e7f6f1e46c11c9cd2edb5041e9b7d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563