regarding Jump leaks, leakers never have a legit insider
they get to look at certain pages of the magazines but not all of it, like the toc page, the anime episodes previews pages, the color pages etc
that's why some tocs leaks lacks what ended and next week cps, they need to go through the magazine for that
that's how the Edited Manga team I used to work with did things back in the day, they don't buy the entire magazine, they just pay a Japanese dude with a scanner for certain pages
regarding anime screenshots and legit leaks, I dunno where they get these from, my guess is hacking studios or tv channels uploads?
maybe their uploads isn't even that protected/hidden in the first place?