Opencv Java - How To Get A Region Of Interest From A Document Image?

I'm trying to get a region of interest from a document image. The region of interest is the signature of the person responsible for the document. I'm using opencv on android to try

Solution 1:

Because it's hard to determine borders of signature itself, you can try find other "stable markers" on document and determine ROI (signature area) relative to them. For example, you can select as "markers" form elements 1, 2, 3 and 4 (red rectangles) find them on document and determine approximately signature positions by calculating normalized distances between them. Assuming, if normalized width and height of image are 100 units, signature area should be approximately 75 "horizontal units" and 20 "vertical units" and its top-left corner should be approximately on (10, 70) position (from top-left corner of form):

Several anchors also needed for "normalization" of document scan by with and height and remove picture rotation (if it exists).