Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f2b5a58dea8c5a816d4f0f5d6ae6d36a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563