>3773c460e43658b17f3e5fe688e10ac3f9a475660518920a92f737fa271c50dc
The trick is in the first few characters of the pic ID.
In this case, it's only "3773" that counts.
View the source of the webpage, and search for "/emailid/" to see what part of the number works. (ctrl-U- in firefox)
You'll see "/emailid/3773"
Just paste the whole pic ID after "https://www.wikileaks.org/clinton-emails/emailid/" and you'll see.
I'm sure someone with more patience could grep and awk something together to get all the ids in one pastebin or something