The most expensive photograph ever sold is just a picture of a river.

Rhein II is a photograph made by German visual artist Andreas Gursky in 1999. In 2011, a print was auctioned for $4.3 million (then £2.7m), making it the most expensive photograph ever sold. In the photograph is a  Rhine flows horizontally across the field of view, between green fields, under an overcast sky. The photograph has been described as a "vibrant, beautiful and memorable – I should say unforgettable – contemporary twist on the romantic landscape" and as "a sludgy image of the grey Rhine under grey skies". It just looks like a picture of a river to me.
http://en.wikipedia.org/wiki/Rhein_II