Apparently, Zoom has both visual and audio watermarking features, making anonymously leaking a recording of a Zoom meeting difficult. The Intercept published a short guide about both “features,” What You Should Know Before Leaking A Zoom Meeting.
The video watermark feature seems straightforward enough,
When enabled, the video watermarking feature superimposes the username portion of each participant’s email address over the content they are viewing when another participant shares their screen and places the same watermark over the current active speaker. Because the video watermark appears across the entirety of the video frame, blurring may adversely impact the visibility of the underlying material.
This is similar to watermarks that might be added to traditional documents. The audio watermarks, however, are insidious because it is not necessarily obvious they are being used; the only indication is a couple of obtuse graphical symbols that are displayed during the meeting.
It is not immediately apparent at what point Zoom injects its “ultrasonic” audio watermark into the audio stream — whether this happens only if a meeting attendee presses the Record button in Zoom or if the audio stream is watermarked prior to that point. Nonetheless, when recording a Zoom meeting, it is best to avoid using Zoom’s built-in recording option and to capture the meeting using a third-party audio/video recorder. Zoom mentions that in order to identify the participant who recorded the meeting, they need at least two minutes of audio from the meeting, though it stands to reason that shorter snippets may also be identifiable if they happen to contain the audio watermark.
The article also does a good job of reviewing issues common to all video platforms. For example, it highlights numerous ways in which recordings that don’t feature either of these watermarking technologies might reveal who did the recording. It is very well worth reading by anyone considering leaking a web conference recording.