Oh boy, that is one spicy topic. You could start here.
In short: The lead dev (who stepped down, but may be back again?) is involved in some controversy.
While I can fully understand why somebody wouldn’t trust the OS based on that, it’s still the most secure and private OS available today IMHO.
Steganography is a (fascinating) bitch. There are a lot of ways to hide a message in an image which is very resilient to manipulations like resizing, compression or even the loss of information by actually filming a screen versus taking a screen capture.
If you adjust your approach to not rely on a single picture to reliably convey a short message, but part it out over tens or hundreds of frames in a video, it’s basically impossible to make sure that the message was erased without knowing the algorithms used or rendering the video unwatchable.
It’s an awesome field and nothing new.