Extent of reuse and reanalysis of data published by others
If you use the figure directly, you'd best get the permissions in line.  If you modify the figure, you most likely don't need to, but properly attribute (i.e., "Modified from...."

My own preference for stuff like this is to use a tool like datathief to grab the data from the figure, and remake my own figure, formatted optimally to make my point.  Attribute the original.