The recognition of check boxes is to understand if exists or less a mark in a specific area or to understand if this are was darked,
This operation is more complex that it looks. Usually is used a threshold (the minimum percentage of black pixels) to determinate the limit between an empty and a full box, but based on filling style, marrking or filling, this threshold can be valid or not. This is why inour system are used two different thresholds, the first to understand the minimum percentage of check mark extension, the second to understand the minimum percantage of black filling.