Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cbcaf7a19406f2c2f6a32b85c06fff0e.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563