One of the most important sources of our knowledge, about Lilienthal's flight technique, is the great number of remained photographic pictures. The 137 known photos from the period from 1891 to 1896, which were made during Lilienthal's flight practise, are documents of the aviation history as well as of the history of photography. By request of himself, Lilienthal, was joined by photographers regularly in order to show the development of his flight technique. The pictures are partly of excellent quality. The most beautiful of his flight pictures Lilienthal used in his annual reports .
Some further photos are in other archives.
All known pictures of the flight practise are listed here. The date of the first successful flight is just as unknown as the date of the two photo serials. Kassner was a meteorologist at the Prussian Meteorological Institute. The members of that institute played an important role in the society. Kassner became a member in 1892 as well.