A rather humble-looking pic has sparked an investigation by researchers into whether this photo is one of the oldest in existence.

There is so little information surrounding The Leaf that scientists have never really got to the bottom of this one. Previously believed to be the work of one of the inventors of photography - William Henry Fox Talbot - in 1839, it may very well be traced as far back as the 1790s.

And researchers say although previously estimated to sell for $US100,000 - $US150,000, it could fetch quite a bit more if it's found to be older.

The historical journey back to the birth of photography continues...