Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/20180b27e5528d11f9c4d9385099ace1.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563