Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/8c28c65b4898138f21a8a1a26db27df2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563