Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f0f91cc8d9ee4c69f2c10dc6d421f47f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563