(1920s) European slums
Dictator(s)/Authoritarian regimes (possible specific examples like Hitler, Franco, or Mussolini)
20th century (early 20th century) medicine/medical treatments/science/doctors/hospitals
Youth culture (in the 1930s?)
Demographics/social class/upper class/lower class/rich/poor
Print Periodicals (2nd floor):
If you want to look at images from the 1930's forward, old issues of periodicals may be useful to you.
History Books (2nd floor):
Since history books usually contain photographs, search the online catalog for history books relating to the era, country, or event you are researching to see images of people in the popular fashions and hairstyles of the era.
Reference Books (2nd floor):
Copyright and Fair Use FAQ from Stanford University's Copyright and Fair Use Center includes extensive information on copyright law, including fair use, the public domain, and academic & educational permissions.
The video below, from the Copyright Clearance Center gives a basic overview of concepts related to copyright law.