Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f1b8e0be4a08c3d08e799d4ad83b14af.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563