Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/4f8f7c0f70e7b4f163a30b51cca24aa7.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563