How to know for sure if a piece of software is 100% libre?
Self-explanatory title. I looked up ImageGlass on the Packages section of Parabola's website and it isn't there, I'm assuming ImageGlass isn't 100% libre? But I don't know how to confirm if it isn't (or confirm any software for that matter.) ImageGlass is licensed under GPLv3, so I assumed it was ok. Anyway, how do I know?
the short answer is that you never really can know, especially with licenses other than GPL - with the GPL, it is conventional to add a copyright header to each source file, indicating that each file is under the GPL - even that is not conclusive really, because it could be a false claim, added to "found code" written by someone else, under another license (or perhaps none) - with other licenses, people will simply add a LICENSE file to the repo, and it must be assumed that it applies to every source file - in the end, unless you personally witnessed the code being written, it is always a matter of blind faith, whether or not the publisher is the sole author, or has respected the copyrights of all collected code
it is often not the case, that a single license applies to every source file; although many developers seem to believe that it does - the GPL for example, explicitly covers "the program"; but does not consider data files, such as images or documentation, to be part of "the program" - any files in a GPL code-base which are not executable source code, need separate licensing, or an appendix to the GPL which covers them explicitly - likewise, the MIT-style licenses explicitly cover "software and associated documentation files"; but presumably, images, audio, and fonts are neither software nor documentation - if any code-base contains files of those type, and does not declare a separate license for them, then that would not meet the test of "free-culture"; and strictly speaking, would make the code-base un-distributable as a whole - often (and probably more often than not), images in some code-base were not created by the author of the source code, but found on the web; but you rarely see attribution, and the typical website where such images are found, rarely mention any licensing, and denote the author only as a nickname - so it is impossible even to investigate, what were the licensing intentions of original author - there is very often no way to contact that person to ask
there is another thread "Building & Modifying Packages" section, asking the same question - most of the answer above is copied from that thread
please refer to that one, and add to it, if necessary
Thank you very much!