title: What is the proper way to test if checkbox is ticked on scanned document?
body: <p>Let's assume, that we're scanning test-like documents with checkboxes / empty circles (for signing / striking / ticking). What would be the proper way, to check, if already cropped checkbox/circle is checked/signed/striked/ticked?<br>
  In case we'll force test users to fully mark the area, just knowing the position of checkbox/circle and counting amount on non-white pixels would be enough (would it?), but what way should we approach to test, that the checkbox / circle is ticked or checked (X)?<br><br>
  This is going to be part of the project in C#, so code or even ready libraries for .net / c/c++ would be appreciated.</p>