A former colleague has created a figure. The figure is not published and serves only as a mean for information sharing. I used to be a part of that research group and thus had access to it.
I published an article featuring a modified version of this figure, to explain my current experimental set-up. I did not cite the author of the figure as the figure was not found in any published material. I didn't know what to do - perhaps add them in Acknowledgments?
Have I done the wrong thing?
The correct thing to do is to cite them for the figure by name, if they will permit it. List the citation as "private communication". You should also probably indicate the it is "adapted from a private communication..."
You have committed plagiarism if you give the impression that you are the source. But it is easy to avoid with a citation.
You can probably handle it in acknowledgements if you are clear about what you are acknowledging. Use language similar to the above.
Citing such "private communications" is often frowned upon, because others can only take your word for it, and have no chance to check the context.
Like with any illustration that you copied or very closely adapted from somewhere else, you put a copyright notice (after asking for the consent of the copyright holder, that is) in a footnote.
The facts represented in such a figure deserve an additional citation, if they were previously published. If not, no problem, but you are automatically taking over the scientific responsibility for their correctness.
I didn't find an information in your text - do your ex-colleagues give you any options they will be satisfied with? Actually, are there some really specific details of the experimental setup, which they patented or invented that are drawn in figure? The question behind that I have - do they claim that this is the case of plagiarism because you published their "intellectual property" or just because you took away the figure that they designed/drawed, although it contains a rather common for your field of research information?
In both cases, I would find the way to solve the problem ASAP during the private meeting to avoid any misunderstanding. In the first case, you need to be careful and, basically, follow their wishes not to escalate the situation you are into.
Good luck with it! Maybe you could update us about the solution.
