This is a rather involved puzzle and might require a bit of stamina. All of the puzzle is in image form. The introduction text is not needed for the puzzle. At the end of the puzzle you'll get a short English sentence. The puzzle consists of several sub-puzzles and you're encouraged to post solutions to the individual steps - I will comment on them.
The puzzles has now been fully solved, and the complete solution is summarized in the accepted answer.
You're in a circular room with a dome-like ceiling. All walls and the floor are bright white. There is only a single, metal door, which has a small, circular whole in eye height. You don't have any recollection how you came here, but at the moment, you're really only interested in getting out. The door, is looked. You knock, and there is some movement behind the hole. Somebody comes to the door and talks through the hole. The voice, however, sound foreign and not very human: "You awake? You out? You say passphrase!"
You are about to ask something, when suddenly the walls behind you begin to shimmer and form a series of images, and the voice through the door adds: "You clever? You find passphrase."
Whatever else you say to your capturer, the only answer you get is: "No, not passphrase."
It seems you really have to find the passphrase. You just hope you can, before you die of hunger and thirst.
On the wall around you, the following images can be found (The appear clockwise around the room starting with the door and ending with the door.)
The following image is auxiliary for convenience sake. It is a close-up of the bottle labels of the 2nd image above.
(Bottle Label close-up)
As always, I'm interested in your ideas and feedback. In particular, I hope the puzzle is fun. If it isn't, let me know why. If it turns out that the puzzles needs amendments or changes to become better, I'll edit them.
The red ABCDEF/1234 labels are not required for the puzzle. They have only been added to make it easier to discuss/describe solutions.
The 6 'rod-shaped' objects in the last image fit in size into the 'slot' of the image with the letters above it. (As shown in the smaller black & white image.)
You may use any tool etc. to solve this puzzle, but it should be perfectly possible to do this with pen & paper alone.
If you are really stuck with this puzzle and are wondering along the lines of "What the @£! am I supposed to solve here??" you may look at the following hints. But they will spoil a bit of your fun (as all hints do.) I try to make successive hints revealing more and more, so just try one at the time...
Where am I even supposed to start this??
The first images until the first horizontal line are called instructions for a reason. Try interpreting them in terms of what is this puzzle about? and what am I to do?
I still don't get it at all...
Remember: At the very end of the puzzle is a pass-phrase. The only image with letters is obviously important, but how could one encode with it - using the previous images? It surely can't be done with one image alone...
But... There are endless possibilities! I could read anything out of this...
Really? Is there no clue about the length of the pass-phrase? Does this length match anything... ?
Okay, okay, so what do I have to solve first ?
The puzzle has 3 main-sub puzzles. Guess what, they are sorted that way. Let's call them the bottles, the scale and the code puzzle. The scale is (literally!) the central puzzle here. It provides the information needed to solve the code. But in order to attempt the scale you need information provided in the bottles. What could that be? Have another look at the instructions! What do the yellow squares symbolize? What does the blue-to-grey shading symbolize? So what could the labels then be for?
All nice and well, but can you give me another hint?
NO. If you are still stuck and don't want to spent more time on thinking, you might as well read the accepted solution below!