Hallo,
I just found a source for tons of bird images on http://www.biologie.uni-hamburg.de/b-online/birds/naumann.htm, and I am eager to use them. But I am not 100% sure, if I am allowed to use them.
All images on that site are drawings from a 1905 field guide, and so they should be public domain. BUT all images were (as they describe on their page) scanned and reworked with a graphics tool in order to change contrast, lightness and hue. I don't know, if this makes the owners of the website new copyright holders.
Of course I tried to contact them, but the e-mail address on that page is invalid, so there is no contact person.
Can anyone tell me, if I am allowed to use these images?
Mirko.