An ExLibris is a small printed graphic work of art with the name of the owner imprinted on it. The first ones were Heralds or Family Crests. They were either on a page bound in a book or as a separate piece glued into the book. These were called "Gebrauchsexlibris", because they were mean to be used. But in the late 1800's and early 1900's, the Exlibris was designed to be collected and was referred to as a "Sammlerexlibris". One would commission an artist to design and print 50 to 100 of these small works of art and then trade them with others. The collector prized the ExLibris belonging to famous people and those designed by well-known artists. These ExLibris would be kept in the collector's library usually in a decorative Box.
Emil Ranzenhofer designed ExLibris for a variety of people with varying topics: historical sites in Vienna, bucolic scenes, and some of a rather risqué nature. Personally, I have come across thirty-four ExLibris by Emil Ranzenhofer. There are two references to him in the Osterreichische ExLibris Gelsellschafte - the XIII Jarhbuch 1915 (p.66 Ada Adler) and the XIV Jahrbuch 1916 (p.69 Dankl).
HG (Heinrich Glucksmann) ExLibris
M.E.d.G. (Marie Eugenie della Grazie) ExLibris
Violette Stokvis ExLibris
The etching of the Donner Brunnen at Neuer Market (Top) and the ExLibris with the name of Alfred Kaufmann. (Bottom) are exactly the same, except that the ExLibris has the name imprinted on it. The etching was probably a stock etching and the name imprinted at a later date.