Authors A, B and C published paper  in journal X.
Author B created a figure for paper . The figure is not essential and does not contain any important data. It is just a geometric ilustration.
Authors C and B are writing a new paper  for journal Y.
Can the same figure be used in paper  without any mention to paper ? Is it ethical? Does it violate copyrights of X? Is it considered plagiarism by Y? How about the situation X=Y?
(Authors A, B and C are friends, so there is no problem for author A.)