That's not the point the other posts are making. They're saying that before encoding the red dot could have been X pixels wide, and to the naked eye it would s

That's not the point the other posts are making. They're saying that before encoding the red dot could have been X pixels wide, and to the naked eye it would seem that after encoding it's still only X pixels wide... but due to compression artifacts it may now actually be affecting an area X+Y pixels wide. So only covering X pixels could leak Y pixels of information. It honestly sounds a bit paranoid to me, but it's definitely possible.