Should I include a reference for an image that is released into the public domain? I am writing my thesis and came across an image on Wikipedia that I would like to use. The licensing on this image is:


  I, the copyright holder of this work, release this work into the public domain. This applies worldwide.
  In some countries this may not be legally possible; if so:
  I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.


Should I still include a reference to indicate this image is not my own work, if so, who should be given credit (the author is not known in this case)?
Should I still include a reference to indicate this image is not my
  own work


YES If the idea is not yours, you need to reference it.


  Who should be given credit


That is a harder question. Ideally, you should find the original author/source. Given a reasonable attempt to find the original author/source fails then reference the secondary/reproduction (i.e., wikipedia/wikimedia).