>Lot 345 of Christie's “Voyage To Another World” auction supposedly has the only photo of Armstrong on the Moon, but isn't this one also?

Yes. 

It is a photograph of Armstrong on the Moon also.

As we have seen in this site the conspiracy theorists who insist that the Moon landings were faked will stop at nothing to look for "Aha!" moments where they believe the've found some issue with a photograph or a temperature or a glove flexibility that "proves" the whole thing was fake.

See:

 - https://space.stackexchange.com/q/20143/12102
 - and all the work that I put into writing two answers to https://space.stackexchange.com/q/31305/12102

### Now imagine if there was not a clear image of Armstrong in this photo? 

There has to be. Armstrong is facing directly into a reflecting surface; Aldrind's [gold-coated heat-absorbing partially reflecting](https://space.stackexchange.com/q/32538/12102) visor.

And of course there is an image of Armstrong in this photograph on the Moon, as there must be!

 - Was the primary target Aldrin? Yes. 
 - Is Armstrong also in the photo? Yes.
 - Is this a photograph on the Moon? Yes.

Q.E.D. This is a photograph of Armstrong the Moon, and there'd be a big problem if it wasn't.

Christie's didn't outright lie, but they do need to qualify their claim that the other photo is the *only photo of Armstrong on the Moon.* Because it isn't. 

Don't ever let people tell you that you aren't seeing what you are seeing.