Hi Janisc
I'm a novice here so how can you tell if the photograph is public domain use?
If you have taken it by yourself, you can release it in the public domain. (Unless some special cases apply. E.g. photos of installations of the artist Christo are still under HIS copyright, once his installation is taken down, at least in Germany. Photos of pieces of art that you do not own belong to the owner in several countries, if the piece of art is young enough.
If you have not taken the picture yourself, you have to ask the one who took it, whether he/she releases it in the public domain.
If you do not know, simply assume that it *isn't* in the public domain. Besides "fair use" is not enough in several wikipedias apart from en.wikipedia.org, e.g. in the German one.
Kind regards,
Heiko Evermann