1. A scanning method for checking transparency of a document comprising: a. a single optical sensor to capture both surfaces of said document; b. illuminating any one surface of said document through an illumination source facing said surface; c. imaging of opposite surface of said document wherein an illumination source facing said opposite surface is turned off; d. processing said imaging of opposite surface of said document in a data processor; said processing comprising i. measuring bleed-through in said imaging of opposite surface; ii. contrasting said measured bleed-through with a measured bleed-through of reference image stored in said data processor.