Should I include a reference for an image that is released into the public domain?

Question

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)?

Answer 1

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).

Answer 2

Here are the recommendations from Wikimedia Commons:

Content in the public domain may not have a strict legal requirement of attribution (depending on the jurisdiction of content reuse), but attribution is recommended to give correct provenance.

Other restrictions may apply. These may include trademarks, patents, personality rights, moral rights, privacy rights, or any of the many other legal causes which are independent of copyright and vary greatly by jurisdiction.

The rest of the page is very informative as well.