...
var
....
R: TRect;
begin
....
ImagenJPG.LoadFromStream(stream);
ImagenBMP.Height:= ImagenJPG.Height;
ImagenBMP.Width:= ImagenJPG.Width;
ImagenBMP.Assign(ImagenJPG);
R.Left:= 0;
R.Top:= 0;
R.Right:= ImageList1.Width;
R.Bottom:= ImageList1.Height;
ImagenBMP.Canvas.StretchDraw(R, ImagenBMP);
....