Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f7835206c59a6b5234f5b1f5cfaf7ad3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563