Would it be unethical to not cite a figure obtained from a Q&A forum? We are writing an article in which we should give a figure (a satellite image; not a real map) to make the 'preliminary' section complete and understandable.

However, drawing the image ourselves is not possible. However, as the image is related to a well-known problem, it is available in various Q &amp; A forums. The same image can be found in multiple such forums and we do not know the original source of the image.

In such a scenario,


Would it be unethical to not cite the forum in our research paper?
If we must cite any of the available forum links, how are we supposed to cite the image?
Would it be unethical to not cite the forum in our research paper?


Yes, of course it would!  Similarly, it would be unethical to use a figure without citation from a student's written exam, a newspaper article, a billboard on the side of the highway, a 3000-year-old clay tablet, or a bathroom wall.  If you do not cite the source of the figure, you are falsely claiming that the figure is your own work.  You must give other people credit for their work, no matter how you find it.


  If we must cite any of the available forum links, how are we supposed to cite the image?


You are supposed to find the original source of the figure, and cite that.  Of course, finding the original source may not be possible, but you do need to make a serious good-faith effort.  (I suggest asking "What's the source of this image?" on the same forums where you find the image.)  If that good-faith effort fails, cite whatever secondary source you believe is most authoritative and/or most likely to be accessible to the average reader in five years.  For example:

[1] Unknown author.  http://three-d-pancakes.ytmnd.com/.  Accessed June 24, 2017.