illustrate vs photoengrave

illustrate

verb
  • To provide a book or other publication with pictures, diagrams or other explanatory or decorative features. 

  • To clarify something by giving, or serving as, an example or a comparison. 

photoengrave

verb
  • To make a photoengraving of an image 

How often have the words illustrate and photoengrave occurred in a corpus of books? (source: Google Ngram Viewer )