I am wondering how to cite a figure that has already been modified from another source. Normally one should get the original figure from the original source, but there are cases when that is not possible or difficult.
Let's say that we find a figure A in source 1. Figure A is a modified version of figure B from another source 2.
So in source 1 figure A it says in its figure text:
...modified after .
Also I am wondering how to cite correctly when I want to modify the already modified figure? Saying modified after again seems quite silly:
modified after  which is modified after .
In addition one should include "with permission", but the following sounds wrong since it appears as if we have gotten "permission to modify":
modified with permission from .
This last example raises the question: does one have to ask for permission to modify a figure in addition to reproducing. Some organizations explicitly tell that no figures may be modified.
So my guess is that it should be formulated as:
reused with permission and modified after .
But this last I can't remember having seen any example of in actual academic papers. What would be the correct approach here?