I took the photograph in 2005 at an dinosaur exhibition held in Citiplaza in Hong Kong. It was marked as "Omeisaurus tianfuensis" . There were 2 other  Mamenchisaurus on display in the same exhibition, they are a very big  Mamenchisaurus jingyanesi and a smaller  Mamenchisaurus constructus. 
 I tried searching the web and confirmed from different sources ([1] and [2]) that they were labelled as such.