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?