WITH Thisform.airgrid1.column1
   .RemoveObject("Text1")
   .AddObject("Check1","checkbox")
   .ControlSource = "Alias.LogicalField"
   WITH .Check1
      .Style = 1
      .Caption = ''
      .Picture = "UncheckedPicture"  && Substitute the name of your picture file
      .DownPicture = "CheckedPicture"  && Substitute the name of your picture file
      .Visible = .T.
   ENDWITH
ENDWITH