Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/906428b9f6b8ee2a851cf3a6ec4f18ac.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563