Use of Copyrighted Illustrations from Prior Publications

Two researchers have co-authored a paper, describing their results, which has appeared as a preliminary report in a copyrighted monograph.  One illustration in this paper is a computer-generated scatter plot of research data.  Both researchers are preparing more substantial papers for submission to peer-reviewed journals.  They both agree that the scatter plot in the monograph article is crucial to their presentations.  Deciding that this illustration must be included in both new papers, they alter their computer program to generate the exact same figure using different fonts and different line thicknesses.  Is it necessary to say in their papers that these figures were adapted from the monograph article?  If so, is that sufficient, or must permissions be obtained?

K5R says:  It would be appropriate to mention that the illustration came from a prior publication, but I don't think permission is required from the previous publication since an illustration itself is not copyrighted.

5S says:  An acknowledgement would be polite, but is not necessary, nor must permission be obtained.  The illustration is not a work of authorship, and is not by itself copyrightable, and is small enough that reproducing it can be considered fair use.

J1G says:  I disagree with the previous comment.  Better to be safe than sued -- it is usually very easy to get permission to reprint any part of an article, or even an entire article.  Just write and ask.  It's more burdensome to come up with a workaround than to do the ethical thing and honor the copyright.