Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cf0a2a4a44956f263e0ed4a2ad4b24eb.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563