Stack exchange publishes the question/answer posts with a credit common license.
In research conference slides, it is very common to use images from papers provided we add a credit, even if the image cannot be shared officially because of the publisher policy. In papers, we don't hack the figures because it is the publisher's responsibility.
SE does not seem to run actively after any image credit violations. There are some discussions on Meta about it (eg. here).
Do you think it would be tolerated to add images in our SE site from papers which are protected under a pay-wall (example in my post here) provided on citing the reference correctly? In research, authors are usually happy to see their figures be used if cited and I wonder if the publishers really care about it. In practice, could we just wait for potential complains or should we strictly not use them?