This has been debunked many times, but it just keeps coming back. Captions used:

• Library books floating down a street during the great flood of Paris 1910
• Books float on the street after a library on Rue Jacob, Paris
• The Paris Library Flood, 1910

The photograph was taken during the Great Flood of Paris in 1910. However, those are not books, but wooden paving blocks. Source: Pavements Like Jelly via London Review of Books.

Debunked by Nick Fitzsimons on Twitter. See also: HoaxOfFame blog entry.