Tooltip can only display text. With the following code in tooltip::show we can also display images and bitmaps.
The user has to provide a valid image/bitmap instead of the message argument.

    # Use late-binding msgcat (lazy translation) to support programs
    # that allow on-the-fly l10n changes
    if {[catch {set type [image type $msg]}]} {
      $b.label configure -text [::msgcat::mc $msg] -justify left
    } elseif {$type eq {bitmap}} {
      $b.label configure -bitmap $msg -justify left
    } else {
      $b.label configure -image $msg -justify left
    }