Kind of ironic to me that the less famous one is the only one with the photo! Ha!
I'd be very surprised if a man of Tenzing's calibre and achievements could not figure out something so trivial.
Edit: I've found some citations that support your point, I apologize.
Although, I'd add (a) Tenzing's account states that he offered to take a photo but was declined. And (b) a more fair description would be "because he had never used a camera before" rather than "didn't know how to work a camera".
The later suggesting a lack of intelligence or civility (though I'm sure that wasn't your intent), I'm probably just nitpicking :-).
This potentially could be a reason as well that he wasn’t brave enough to admit.
That theory doesn't make sense to me.