Old post, but adding an answer for new visitors.
It's interesting that many beginner piano methods do not show a piano keyboard labeled with the pitch letters. I'm sure those methods assume a teacher will explain that. But, Czerny's methods The Young Pianist op 823 and Complete Theoretical and Practical School op 500 do show labeled keyboards...
A lot of people recommend against actually labeling the keyboard, but there is some logic behind it, as some methods provide labeled keyboard pictures.
You could consider putting a printout on the wall or in one of those plastic sleeves to keep on the music stand for reference. The OP's linked keyboard image is not good, because it labels all the black keys with sharps only. It should have sharps and flats.
There is a reason to not label the keys. Consider, for example, key number 42, the white key above middle C. As a natural it's a
D, but it can also be
C double sharp, or
E double flat. Most beginner's material won't use double sharps or flats, but those do occur in real scores. If the idea sets in the beginner's mind that keys have fixed pitch letters - actually labeling keys with letters will promote that - the flexible naming of keys with sharps and flats could be confusing to learn later on.
A compromise option could be to just label the key for middle C to get a reference point. If you use masking tape on the key, you can write on the tape and then remove it later, so your keyboard is not permanently marked. You could also mark the
Cs at the octave above and below to help reinforce the repeating of keys at the octave.
Sight reading children's five finger exercises is common at this beginner stage. Learning the pitch letters is obviously important, but you should also start learning to read intervals at the beginning too. Like, five spaces/lines up from middle C (in C major, staff with no key signature) at the keyboard means five keys up from middle C on the keyboard, which will be
G. Reading those steps up the staff/scale is just as important as knowing the letter is
G. In fact, after the beginner stage, reading staff as intervals rather than letters, is the better way to approach reading scores.