It’s called ACR data and it’s very common. And yes, TVs are phoning home with it.
And GDPR only requires that you opt in. So when you sign into the TV for the first time, it gives you an opt in choice and many do it. The States is less regulated but will be soon.
These are of course just guidelines, but if you don't explicitly inform your users that you will be sending images of what's on the screen over the Internet, you are likely to get in trouble. (And no, a giant EULA-type wall of text probably wouldn't be sufficient)
It isn't nearly as easy as you're suggesting to escape the scope of GDPR protections. There could be sensitive personal data or data about children involved. Even if it's just some identifiable individual in the screenshot, you still can't just rely on some sneaky "consent" as a blank cheque - that is merely a possible lawful basis for processing, and all the other provisions of the GDPR still apply.
Edit: Also, on your first point, ACR is generally a variation of fingerprinting technology. It wouldn't be sending entire screenshots of whatever is being displayed even if it's not broadcast content, at least not in any variation I've heard of. It was the idea of uploading the entire image that I was questioning before.
Fair point on the screenshot. Yea I dont think any TV is phoning home with screenshots. Rather it's phoning home with a processed signal of the A/V in order to ID that A/V. If there is A/V that cannot be recognized, it may phone home a screenshot of that.
And I also don't think it's easy to escape the scope of GDPR. I'm just saying companies come up with ways of being "GDPR compliant" and they've done so.
And GDPR only requires that you opt in. So when you sign into the TV for the first time, it gives you an opt in choice and many do it. The States is less regulated but will be soon.