Could a civilization 600 light year away detect our planet and reveal its composition

And possibly figure out if life exists here with our current level of technology?

It depends, I presume you refer to Kepler 22b, it is possible that there is no life there, it is possible there are creatures like neanderthals, or they could be 1 billion years more advanced than us and watching our planet right now(though they would see it how it was in 1200)'
If they are intelligent enough they could have telescope that can read size one font from 500 light years away.

If _their_ technology is advanced enough that the could analyze the light reflecting off earth and determine the composition of our atmosphere, they could infer at least the possibility of life here on earth, even without waiting to pick up broadcasts of "I Love Lucy".

(I should point out that we're probably not that far away from being able to do that with at least some planets. I'm in my mid 40's, and I wouldn't be surprised if we figured out how to do it in my lifetime).

The large amount of oxygen in our atmosphere would be the clue. Oxygen is reactive enough that it wouldn't exist in large quantities in our atmosphere without it being continuously replaced somehow.

Even if their form of life is based on totally different biological processes, finding that much oxygen would surely raise some serious red flags in their scientists minds about what put it there.

If they're advanced enough, sure they could detect us and possibly see us better than we can see ourselves with google earth and such.

About the current level of technology.. they MIGHT be seeing us as we were, 600 years ago. (circa year 1411). That's before Galileo and Sir Isaac Newton!

Then again, this answer is biased from a human from earth. Theres no universal law that states they would have the same 600 light year lag we would. Their technology could provide a live image even though they are 600 light years away.