recognition and blocking of advertising on TV

5 years ago I noticed that a second before the start of advertising on the TV screen, the channel icon in the corner disappears. Is it possible to make a special filter / decoder / analyzer that will recognize the presence or absence of a channel icon and, depending on this, give an image from a channel, or from some other source (weather forecast, news, a webcam from the street, etc.) P.)
Also interested in the question, from a legal point of view, such a device would be legal and would not violate the rights of the owner of the TV channel?