@pablousavilla Not sure if you;re still having troubles with the camera, but I ran into the same thing. the one way mirror significantly darkens the image. In my case, the mirror has a frame so I drilled a tiny hole, painted it black, and routed out the back of the frame so the camera was flush to the frame face.
That helped, a lot, but in the dark, still wasn’t enough to recognize faces.
So I switched to the NOIR raspi camera, then added a couple of IR Leds. The image from the NOIR camera won’t win any awards, but that’s ok. it’s just for motion detection and face reco, and that works great now, regardless of whether the lights are on or off. just train it with a decent sample set.
With yours, since there’s no frame, it might be a bit trickier. I found that the one way mirror reflected a TON of IR light, too much to get a good picture from the camera if the camera was located behind the glass.
You might try some IR lights behind the glass and mount the camera below the bottom, tilted up. Or maybe replace one of the mount bolts with a “fake” that has a hole for the camera.