This image previously appeared in Terry Bennett's "History of Photography in China: Western Photographers 1861–1879", published by Bernard Quaritch in 2010, with the caption:
Fig. 1.20. William P. Floyd. ‘Five Storied Pagoda, And Old Fort, Canton,’ c.1870. Numbered ‘34’ on the photographer’s printed label. Author’s Collection.
See http://gwulo.com/node/35363 for more information.
It is reproduced here with the permission of the author and publisher.
Date picture taken
Re: Zhenhai Tower (鎮海樓)
This is the Zhenhai Tower (鎮海樓), Five Storied Tower (五層樓) is its nickname (literally). The Guangzhou Museum link is sort of out of date though.