I don't think the picture of Jack looks particularly like John Barrowman, and the picture of Martha is mainly recognizable in the hairdo rather than the face. People would not recognize K-9 walking down the street.

Other than Rose, the single most recognizable image in the book is that of Joan (and her grand- or great-granddaughter). Having a friend whose resemblance to her paternal great-grandmother is quite uncanny, I can buy that resemblance.