Is This The Original Envelope?

Is this the original envelope?

If genuine, why does not carry cancellations

How about a scan of the stamp.

It looks like a bisected 1858 Danish stamp.
Altona is/was part of the city state of Hamburg.

Looks bisect with pen/manuscript cancel. Could be very nice if all proper usage although not somehow being tied to cover may void the potential. Closer scan of corner with stamp will help.

Altona was incorporated into Hamburg in 1937 only, before it was part of Prussia (since 1868), and still before it was Danish. So the Danish stamp seems quite OK, apart from the fact that apparently it was not accepted being bisected? The blue 2 would be the postage due from addressee.

The cancel looks like 1871...does that change the circumstances for the Danish stamp?

I agree with you Cjd about the date being 1871 which would make sense
since the German Empire was inaugurated in January 1871 and
the postcard is imprinted with Deutsche Reichspost (German Imperial Mail)
Therefore since Altona/Hamburg/Prussia were in 1871 part of the the German Reich which did not issue stamps until January 1,1872 the stamp which should have been used were those of the Norddeutscher Bund (North German Confederation) to which both Hamburg and Prussia belonged to after 1867.

Which invalidates the Danish stamp and that is why there would be postage due if that is what is meant by the blue 2 as mentioned by Heinz.

If there was something that tied the Danish stamp to the card, it would be interesting to me, but the seeming lack of any tie makes me wonder if it is not a concoction. (In which case, it would still be interesting to me if it came in an assortment, but I wouldn't seek it out.)