Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/503edd43f5c8947f64851bf4e64f1dd4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563