A Two-Step Method for Ensuring Printed Document Integrity using Crossing Number Distances
Résumé
Nowadays, with the use of photo-editing software being mainstream, document integrity verification has become crucial. As we have seen during the pandemic, most administrative documents are printed and then scanned before being transmitted, making these documents noisy. Indeed, a printed and scanned document undergoes geometric transformations, as well as the addition of black spots, not to mention a decrease in color intensity. The relevant features of an original document, which will be matched against a query document, are stored to be used as a template. We propose a 2-step method that compares a template with a query document to ensure that the query document has not been tampered with. Our method first reverts geometric transformations the document underwent, and then extracts the crossing numbers in that image. A Euclidean distance based matching method is applied to the two sets of crossing numbers, and abnormally distant point groups are flagged as potentially modified. A second step in our method is then applied to analyze the statistical properties of these distance values, to ensure that the document has not been altered. Our results when we apply our method to a database containing administrative documents and tampered versions of these documents - all of which underwent a print and scan process - show the validity of our considerations.
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