Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f1439c5b0d25d76f9b6fd3ea42d48aa2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563