Then the two photographs could be compared to say this is how it was, and this is how it now is.

The book Final Conflict (L.Ron Hubbard) presented a practical application of your summation (it was not in the movie).

In the movie, we see world of the invaders blowup like there was a lampost camcorder sending pictures back.

In the book, the earth hero (John?), did not witness the desruction of Tyrell's planet directly. But, he did have acces to the orbital systems around Tyrell's planet.

John wanted to assure himself (in the book version) that the planet had actually been destroyed. How did he do that (in the book)?

He caused oned of the satelites that orbited a great distance from the planet to accelerate away from the planet a multiples of the speed of light until it caught up with the photons that had the information he wanted, the explosion of Tyrells planet.

Time is the same all over the place - but when we look at the sun, we see it as it was eight minutes ago. SO what we see, when we look at the sky, is not current events, but history:-)