Collage created from the following files on Wikimedia Commons, each of which is in the public domain or otherwise freely licensed:

• 
  Moritz Schlick –

  Public domainPublic domainfalsefalse

  This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 70 years or fewer. You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.  Note that a few countries have copyright terms longer than 70 years: Mexico has 100 years, Jamaica has 95 years, Colombia has 80 years, and Guatemala and Samoa have 75 years. This image may not be in the public domain in these countries, which moreover do not implement the rule of the shorter term. Honduras has a general copyright term of 75 years, but it does implement the rule of the shorter term. Copyright may extend on works created by French who died for France in World War II (more information), Russians who served in the Eastern Front of World War II (known as the Great Patriotic War in Russia) and posthumously rehabilitated victims of Soviet repressions (more information).

  This file has been identified as being free of known restrictions under copyright law, including all related and neighboring rights.

  https://creativecommons.org/publicdomain/mark/1.0/PDMCreative Commons Public Domain Mark 1.0falsefalse
• 
  Otto Neurath –

  Public domainPublic domainfalsefalse

  This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 70 years or fewer. You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.  Note that a few countries have copyright terms longer than 70 years: Mexico has 100 years, Jamaica has 95 years, Colombia has 80 years, and Guatemala and Samoa have 75 years. This image may not be in the public domain in these countries, which moreover do not implement the rule of the shorter term. Honduras has a general copyright term of 75 years, but it does implement the rule of the shorter term. Copyright may extend on works created by French who died for France in World War II (more information), Russians who served in the Eastern Front of World War II (known as the Great Patriotic War in Russia) and posthumously rehabilitated victims of Soviet repressions (more information).

  This file has been identified as being free of known restrictions under copyright law, including all related and neighboring rights.

  https://creativecommons.org/publicdomain/mark/1.0/PDMCreative Commons Public Domain Mark 1.0falsefalse
• 
  Hans Hahn –

  
  

  This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

  You are free:

  • 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.

  https://creativecommons.org/licenses/by-sa/4.0CC BY-SA 4.0 Creative Commons Attribution-Share Alike 4.0 truetrue

Alfred Jules Ayer –

Public domainPublic domainfalsefalse

This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 70 years or fewer. You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.  Note that a few countries have copyright terms longer than 70 years: Mexico has 100 years, Jamaica has 95 years, Colombia has 80 years, and Guatemala and Samoa have 75 years. This image may not be in the public domain in these countries, which moreover do not implement the rule of the shorter term. Honduras has a general copyright term of 75 years, but it does implement the rule of the shorter term. Copyright may extend on works created by French who died for France in World War II (more information), Russians who served in the Eastern Front of World War II (known as the Great Patriotic War in Russia) and posthumously rehabilitated victims of Soviet repressions (more information).

This file has been identified as being free of known restrictions under copyright law, including all related and neighboring rights.

https://creativecommons.org/publicdomain/mark/1.0/PDMCreative Commons Public Domain Mark 1.0falsefalse