how to check answer paper of OMR sheet

Question

Hi, I want to Develop a application, Which will help To Check Answer Paper (objective Question). Answer Paper Will have Objective Questions. See, Answer paper will contain some Bubbles like circle for each Option, Suppose

 Q1 a() b() c() d()

 Q2 a() b() c() d()

 Q3 a() b() c() d()

  Q4 a() b() c() d()

Student will Read Question paper And fill the bubble on answer paper. Suppose my answer to question 1 is C so i will fill that bubble with ink or mark it.. Now all the mark answer on answer paper should be scanned and should be recognized by software. and then compare with other values.