I've been engaged in trying to solve "The Fischer Mystery" (to be covered in an upcoming entry). One of my discarded leads caused me to stumble upon a rare image.
That's the cover of Wilhem Fischer's Dämonische Mittelwesen, Vampir und Werwolf (Stuttgart: Strecker and Schröder, 1906).
Early 20th century non-fiction vampire books are quite sparse. Off the top of my head, I can only add Stefan Hock's Die Vampyrsagen und ihre Verwertung in der deutschen Litteratur (1900) and A. Osborne Eaves' Modern Vampirism: Its Dangers, and How to Avoid Them (1904) to the list. Dudley Wright helped get the ball rolling in 1914, and even then, it was still slim pickings till Montague Summers hit the scene.