This picture was emailed to me by the Vaad Lishkas Ha Kodesh. It is a mezuzah that was printed on klaf and afterward the sofer wrote on top of the printed word. This is called ksav on top of ksav, and is assur (forbidden) according to EVERYONE! This issue is really an outgrowth of a topic that the Vaad Lishkas Ha Kodesh brought up several years ago. At that time it was found out that there were people who were silk screening tefillin, mezuzos, and even torah scrolls. They wrote a long article which included the opinions of many many poskim that this was forbidden.
If you look closely you can see where the printed letters still show underneath. Also, and even more obvious is the perfect spacing, and perfectly consistent lettering. Notice how the exact same amount of space is between each letter, and between each word. Even the best tefillin and mezuzos have slight variations in spacing. Even top quality lettering is doesn’t come out like a computer font (I believe that the hand written quality is actually nicer than a computer font, just like real art will always be nicer than computer generated art). It’s just a bit too perfect and consistent. Human beings just can’t write that perfectly!
I’m guessing that your question is, ” If the sofer still has to write all the letters, what does he gain?” The answer is simple. If I could write two and a half (good quality) mezuzos in a day without using this trick, I’m sure I could write five or six mezuzos using it! That’s a pretty big increase in profits! On top of that, I would completely eliminate the possibility of making a spelling mistake. Remember, if the sofer makes a spelling mistake and doesn’t catch it, the whole mezuzah is possel, and if he does catch it before he writes Hashem’s name, he will have to spend a lot of time fixing it, and he will likely have to lower the price of the mezuzah if he doesn’t do a really careful repair.