if Picture.Graphic is TJPegImage then
begin
  bs:=TBlobStream.Create(TBlobField(Field),bmWrite);
  Picture.Graphic.SaveToStream(bs);
  bs.Free;
end
else if Picture.Graphic is TBitmap then
begin
  Jpg:=TJPegImage.Create;
  Jpg.CompressionQuality:=...;
  Jpg.PixelFormat:=...;
  Jpg.Assign(Picture.Graphic);
  Jpg.JPEGNeeded;
  bs:=TBlobStream.Create(TBlobField(Field),bmWrite);
  Jpg.SaveToStream(bs);
  bs.Free;
  Jpg.Free;
end 
else 
  Field.Clear;