It'd probably be much easier to just blur the area of the image where they put it to be honest, I've seen this on streams before, they just blur the bottom corner where the number would show up.
Although the position of the number is (obviously) under the control of the platform operator, so could appear anywhere, for any amount of time, if they were so minded.
I wouldn't like to bet against the number appearing right in the centre of the screen for a fraction of a second, if there were any particularly high-value programming being illegally streamed.
