Spoiler:It was Leon Kowalski's apartment that he searched (the heavyset replicant who fails the Voigt-Kampff test at the beginning of the film and gets shot by Rachael). Deckard got the address, I believe, from Kowalski's job application to the Tyrell corporation.
Zhora was a replicant. Replicants bleed just like "real" people. The woman in the photo is supposed to be Zhora, but it's not clear because they used a different actress, in a wig headscarf. (To make it even worse, the picture he prints out does not match the image on the monitor. Very poor attention to continuity.)
I forget how the photo of Zhora is supposed to fit into the investigation. Does Deckard use it along with the snake scale to locate and identify her? (Ah! A look at a transcript shows that he notices the sparkling scales on a dress next to Zhora in the photo, which makes him realize why he found a scale in the tub earlier.) The whole investigation is somewhat haphazard. Harrison Ford has always said that his biggest challenge in that movie was trying to give some direction to a detective who never really does any detection.
The script
is confusing, partly because the story kept changing during filming and even later. The shooting script was cobbled together out of several different drafts, along with bits that were pretty much improvised. Many of the different versions are available at
http://www.brmovie.com/Downloads/Docs/BR_Scripts.htm
