Recording technology exists in many genres, including modern and most science fiction settings. Players will generally expect that whatever is recorded is true - that it really happened as reproduced on the recording. You can mess with this in a fews ways:
- The recording could be a true recording of events, but the events were staged. It was actors pretending to carry out an assassination, with an actor with an explosive fake blood pouch pretending to have been killed. In this sort of untruth, there are no technical details of the recording that can be used to discover that it was faked, because things like digital noise levels or colour balances represent a real scene and have not been modified after recording. There may be other clues, such as the blood pouch being visible, or it exploding a frame before the "shot" was fired.
- The recording could have been tampered with. There was a true recording, but it has been edited to remove or add certain crucial details. In this case there may be technical clues such as the noise levels or colour balances that don't match between the original and doctored parts of the video.
- The recording could have been corrupted naturally by something. Technology doesn't last forever. Files get corrupted. Analogue media lose fidelity every time they are copied. Physical media get mishandled, scratched, degaussed, unspooled, broken, scorched, whatever. Some parts of the recording might be viewable, some could be partly understandable, and other sections might be lost forever.
- The recording was never high fidelity to begin with. The resolution, light levels, or audio reproduction just aren't good enough to make out some important detail. And Hollywood video processing notwithstanding, there's no magic "enhance" button that can fix it.
- The recording is on an obsolete medium. If someone gave you important information recorded on a cassette tape today, how would you read it? What about an 8-track tape cartridge? A gramophone cylinder?
- The recording contains vital information in a different language. It could be a relatively simple one to deal with, such as Russian or Japanese. Or it might be Akkadian or Ancient Egyptian. Or something that linguists can't even identify.
- Critical parts of the recording, or perhaps even the whole thing, are encoded. This could be a simple code or cipher, a constructed language, or some sort of encryption method. Things at the simpler end of this spectrum could be breakable, with more or less difficulty. Simple encryption might be crackable with a large but potentially feasible amount of computing power, while advanced encryption may be completely uncrackable and require social engineering to access the encryption key.
- The recording could be being recalled by a character. They saw the recording a while ago and now have to communicate something about it to someone else. But their memory of it isn't perfect. Like R2 here.
Commentary by memnarch (who has not seen the movie)
Hmmmmmmmmm! Maybe there is something to the nostalgia angle for the movie plot? It'd be exceptionally difficult to fake this scene using previous movies' images. The Irregulars would have to put a ton of effort into editing the background out from the transparent Leia without completely wrecking the image, then plausibly put it into a scene between Luke and R2-D2 on the ship. This'd also work fairly well for the "wanting simpler times" nostalgia bit considering that Leia was just exploded as well.
Ok, movie guessing time, starting with that assumption a few comics ago that Luke's not done anything so far except try and get Rey to leave. Luke sneaks aboard to see the Falcon again and runs into Artoo. The old Leia message from Episode IV plays after he's been wandering around the ship and talking to himself about things. Luke gets a change of heart from seeing the hologram and actually starts training Rey, or at least goes with Rey back to the Resistance. That actually seems simple enough to be very plausible, especially since that could also fit into any other mainstream kind of movie with an old mentor.
Maybe that's too simple of a summary though? I've been told I way over-think things sometimes, which is probably quite accurate, but this guess could also be over-compensating in the other direction. Over-thinking is actually really easy to do with seeing the movie panels slowly like this. At least with the first six movies, I had some idea of where the Irregulars' plot had to end up!
R2-D2: Anyway, speaking of nostalgia, look what I found while I was defragging my storage.
[SFX]: < pating pip bop pow bip-deep beepop cheep >
R2-D2: I project the old hologram of Leia from Corey’s first adventure. Annie, do you want to do the audio?
Finn: I don’t know if I can recall it word for word...
R2-D2: Never mind, I remember it.
R2-D2 (Hologram Leia): I obviously can’t do this super important job myself. Whereas you, R2, are a superior being.
R2-D2 (Hologram Leia): Get these plans to Senator Binks on Naboo.
R2-D2 (Hologram Leia): Oh, and take 3PO with you. Keep her out of trouble. I know I can trust you and your exceptional skills.
Finn: That’s... not exactly how I remember it.
R2-D2: Well, I knew what you meant.