Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2c2b3082ddb4c3e1d5e1a44a8a7e55c8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563