Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/4f11c8d2e6ca9e93c72f2f43d2e1a7a6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563