They only want an uncropped ingame (F2) screenshot because that will show today's date in the Invaded scoreboard, which they can cross-reference with the file's date metadata, as well as using that to prove that the image did, in fact, come from Invaded (as opposed to you just spawning in the messages in a creative world with tellraws)Yes I had the timestamps, but I'm guessing they can be faked, I don't know.
timestamps are used by staff to narrow the search in logs, so no. basically server side logsYes I had the timestamps, but I'm guessing they can be faked, I don't know.