We’re talking about fingerprinting stuff coming in via HDMI, not stuff being played by the “smart” part of the TV itself from some source.
You would probably not need to actually sample images if it’s the TV’s processor that’s playing something from a source, because there are probably smarter approaches for most sources (for example, for a TV channel you probably just need to know the setting of the tuner, location and the local time and then get the data from available Program Guide info (called EPG, if I remember it correctly).
The problem is that anything might be coming over HDMI and it’s not compressed, so if they want to figure out what that is, it’s a much bigger problem.
Your approach does sound like it would work if the Smart TV was playing some compressed video file, though.
Mind you, I too am just “thinking out loud” rather that actually knowing what they do (or what I’m talking about ;))
So by Israel’s own standard of discourse, they’re “using human shields” and hence any amount of killing of Israeli civilians is perfectly justified not matter how great the disproportion of civilians to non-civilians killed, their age or gender.