Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/20a1ed95a3ae7f6442bc9e4d1d7efbdd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563