Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a68fbd9bc07cec9701983b6f5e3288d0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563