I would use options buttons instead of check boxes. This avoids someone checking both boxes.
Not very elegant, but I don't know of a way to actually get the picture out of the control otherwise:
Private Sub CommandButton1_Click()
Dim oRng As Range
Dim oILS As InlineShape
Hide
Select Case True
Case optA: SavePicture Image1.Picture, "C:\TempPic.bmp"
Case optB: SavePicture Image2.Picture, "C:\TempPic.bmp"
Case Else
Exit Sub
End Select
Set oRng = ActiveDocument.Bookmarks("Picture").Range
oRng.Delete
Set oILS = oRng.InlineShapes.AddPicture(FileName:="C:\TempPic.bmp", _
LinkToFile:=False, SaveWithDocument:=True)
Set oRng = oILS.Range
ActiveDocument.Bookmarks.Add "Picture", oRng
oILS.Width = Image1.Width
oILS.Height = Image1.Height
On Error Resume Next
Kill "C:\TempPic.bmp"
On Error GoTo 0
Set oRng = Nothing
lbl_Exit:
Exit Sub
End Sub