Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/50f609f6378b1b17fe9fa715f977ae1f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563