lithograph vs watermark

lithograph

noun
  • A printed image produced by lithography. 

verb
  • To create a copy of an image through lithography. 

watermark

noun
  • A translucent design impressed on the surface of paper and visible when the paper is held to the light. 

  • A mark indicating the level to which water has risen. 

  • A logo superimposed on a digital image, a television broadcast, etc. 

  • A value stored in a datafile to ensure its integrity, so that if the file's contents are changed then the watermark will no longer match the contents. 

verb
  • To mark paper with a watermark. 

  • To mark a datafile with a digital watermark. 

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