Yes, they can. The most pernicious version literally sends compressed screenshots to their data-harvesting services. Compression can be pretty aggressive, since

Yes, they can. The most pernicious version literally sends compressed screenshots to their data-harvesting services. Compression can be pretty aggressive, since they only really want to figure out what you’re watching, and they have a full database. This process is essentially a hash-table of screen content; they can use compression on screenshots because that hardware codec is heavily optimized and quite cheap (witness mobile streaming video usage). I have no idea which vendors/models currently do this, but several have been caught doing it in the wild; it’s not just theoretical. Things like pi-holes and avoiding ever ‘activating’ your smart tv can help stop it, but if you want to use the built-in Netflix (etc) app, or look for firmware updates, or use a built in Roku or similar, then you’re usually either doing something complicated (routing rules, pi-hole, etc) or giving in to your tv collecting data on you.