Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d3fbc7cdd1e6f00b72ea9ee241d0c7e8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563