I have already explained how B. I. tells the reader not to look at the picture, but at the book; perhaps the matter may be still more clear if I give a paraphrase of the verses.
TO THE READER.
The dummy that thou seest set here
Was put instead of Shake-a-speare;
Wherein the graver had a strife
To extinguish all of Nature's life.
O, could he but have drawn his mind
As well as he's concealed behind
His face; the Print would then surpasse
All, that was ever writ in brasse.