I wonder if Sky Q just uses one thumbnail for all showings of Millionaire, whether they're on ITV, Challenge, or Sony Channel? If so, I wouldn't be surprised if this applies to other shows too - like ITV3's Coronation Street and Emmerdale airings (the thumbnail would probably have the current casts and not the ones from 30 years ago).
I don't think so, Challenge's image is of Tarrant. (The current Corrie/Emmerdale episodes update with shots from the episode, while the Classic's just show the Emmerdale and Rovers signs)
“Nostalgia’s cool, but it won’t help me now, the dream is good, if you don’t wear it out.”