Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2728d91ea6ebf7e57d983c87d50f8b2e.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563