Just noticed this thread,i doubt that any kind of photo is from 1827 as the camera hadnt been invented then!Also the zoo wasnt open the public at that time and the first hippo didnt arrive until 1850,The earliest known zoo photograph is of a sheep paddock at the Jardin des Plantes,Paris [1851].As for the John Edwards book it took him about a dozen years to sell out-so if you havent got it you have only yourself to blame [he only sold out last year].
Actually, the earliest known photograph (or "heliograph") dates from 1822
One of the best books on early London Zoo that I've come across is the "Zoological Society of London", by Henry Scherren, dated 1905. It's downloadeable for free, and virus free, here:
Internet Archive: Free Download: The Zoological Society of London : a sketch of its foundation and development, and the story of its farm, museum, gardens, menagerie and library
Lots of lovely old watercolours within, as well as some photos, if I recall rightly.