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;