No need for alarm...
It's true that if you left the TV on the same strong image for a period of time, you could burn that image into the tube permanently.
But for any normal household with changing channels and the TV only on a few hours at a time, it's very unlikely.
Video games can be offenders, because they tend to have fixed graphics.
You can sometimes see the effect in bank cash machines or in - for example - the monitors in our local railway station, which have the ScotRail logo burnt in permanently.
I would also be wary of the 4:3 setting over a long period of time, which could leave marks at the edge of the picture.
But the best advice is enjoy your TV, change the channel or image once or more a day and you should be OK.