@AliceD I would imagine that using images from non-open access journals, when properly cited and linked, is covered under fair use, but IANAL. I don't know if we would have to ask for permission to "re-publish" them. I doubt that anybody will get too bent out of shape, though.
@MattDMo I had to google IANAL :) I am not either, but intrigued by copyrights etc. I will probably continue taking pdf snapshots and adding them here without permissions from the journal or authors. It doesn't happen that often, most images can be easily obtained on the web without accessing paywalled articles via uni libraries anyway.