I think it's suffice to say that the word of the guru or the shabad is to be the eternal guide.
On another note , that you should understand is that most non -sikhs, when they meditate have some sort of a guide to aid them.
In my case, I usually prefer to picture an image of Guru Nanak when I start meditating. I see it as my personal guide to aid me on my journey and I'm sure most others have something similar.
What is the true picture as image of Guru Nanak?
If one carefully understands the essence of Gurbanee then one finds the
true image of Gur Nanak is that of the JOTi image of the CREATOR itself.
So try to know the true image of the CREATOR.
But I am sorry to say we dont believe that there is some image of the CREATOR ( Every one says there is no image of the CREATOR)
Once the image of the CREATOR is known it would be very easy to see Gur Nanak before you.
Prakash.S.Bagga