to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
The author of this image from Switzerland is unknown, and the image was published at least 70 years ago. It is therefore in the public domain in Switzerland by virtue of Art. 31 of the Swiss Copyright Act.
Note that this applies only if a reliable source is cited to indicate that the author is not publicly known; just not knowing who the author is is not enough to qualify the image as public domain. This image may not be in the public domain in countries other than Switzerland.