Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/bb13638ea6e0e0f9507b74d1c8e629ac.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563