Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3ac4cbfd1904f3e03e95b0dbcaa9f93a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563