Is it worth it?
The "Rhein II" was taken by Andreas Gursky in 1999 and sold november 8, 2011 at Christie's New York.
A photo (or anything) is worth as much as someone is willing to pay for it so, for the new happy $4,3 MILLION photo owner it was worth it but, for you and I, probably not.
Edit: I just want to add this... The "Phantom" is a photo made in 2013 by Australian-born photographer Peter Lik. If true this print was sold to a private collector for $6.5 million which would make "phantom" the most expensive photo ever sold.
However, many in the industry have expressed skepticism over the claimed sale price and that the alleged sale was handled privately, instead through an auction house or gallery and that no documentation had been provided to confirm the sale and the 6,5 million sales price. The most expensive and confirmed photo is the "Rhein II" above as for what i know.