I'm writing an editorial and would like to use a figure that I published with a coauthor a few years ago.
The copyright agreement (see #4) with the publisher allows the authors of the paper to reuse any of the work in any derivative work, as long as proper attribution is given, including a DOI.
Given the above, I would have permission from the publisher to include this figure in the editorial with proper attribution.
The coauthor and I, however, have had a falling out, and if I did ask permission he would almost certainly say no. He did not make the figure for the paper, I did, and I am first author.
Given that I produced the figure, and the publisher would allow me to use my work in any derivative work, am I required (even ethically) to ask permission of my coauthor to publish this figure in an editorial that I'm writing?
More generally, when copyright terms from the publisher are such that the author(s) may use their work in derivative works (with proper attribution), as is common in my field, must authors always obtain permission from all coauthors to republish orginal or derivative works?
I don't think that it matters who created that figure or any particular internal to the paper artifact. The copyright AFAIK applies to the paper as a whole (would it be a data set, things might be a bit different). Since the paper is a joint work (legal term), even though you're a first author (academic term), from a legal standpoint, you are a co-author and, thus, IMHO your association to the specific artifact is irrelevant. Ethically, I think it would be OK to use a part, solely created by you, without the co-author's permission (not sure how helpful is that, considering the legal aspect).
Having said that, perhaps, you can use the figure in question in an editorial, based on the fair use legal doctrine. I would recommend to consult with your institution's legal department in regard to assessing the interpretation and applicability of the fair use doctrine in/to your particular case.
Disclaimer: I'm not a lawyer and this answer does not represent a legal advice.