GPL must be applied on screenshots of GPL software or not. Can a screen recording of GPL software, such as Linux, be published?
The question you need to be asking here is whether the picture/screen recording is a derivative work of the copyrighted material or not. In general, the answer to this is "no" (and this is independent of license) - a program compiled with
gcc is not a derivative work of
gcc, and a document created with Microsoft Word is not a derivative work of Microsoft Word. If the output isn't a derivative work of the copyrighted material, the license of the copyrighted material is irrelevant, and you can distribute it under any license you like.
Probably the most common situation in which in may be possible for a picture to be copyrighted is if it includes significant graphical assets - for example, I couldn't take a screenshot of Super Mario Bros (or Freeciv if you want a GPL example) and then distribute that under an arbitrary license, although various fair use/fair dealing exceptions may apply. You can think of other examples in which the output is subject to the original license - e.g. quines.
It depends on how the software is featured in the image whether the image can be considered a derivative work or not and if copyright exceptions apply or not. If the image is a derivative work and no copyright exceptions apply, then it must be licensed under the GPL license.
For an image to be a derivative work of something else, that thing must be the main thing being depicted in the image. So, a screenshot or photo showing only a text editor with Linux code is most likely a derivative work of the shown portion of Linux code. On the other hand, a photo of a study with a monitor in the background showing Linux code is not a derivative work of the Linux code.
And then there is a class of derived works where you don't have to abide by a copyright license, and that is if your work falls under the Fair Use (or similar) exceptions in copyright law. A most notable example of Fair Use is when giving critique. In such cases, Fair Use allows you to reproduce parts of copyrighted works that would otherwise be in violation of the license terms.