title: removing noise from document images
body: <p>I'm working on a project to automatically process scanned invoices. In order get a better result the OCR engine, I'd like to first remove noise from images. Beside scratches, I'd also like to remove anything that was added to document after it was printed. Many invoice e.g. were ticked off and sometimes it makes parts of the invoice unreadable for OCR. </p>
  
  <p>For example have a look at <a href="http://www.rctech.net/forum/attachments/r-c-items-sale-trade/725795d1300678269-like-new-slash-4x4-platinum-w-novak-havok-pro-sct-4-5t-invoice.jpg" rel="noreferrer">this</a> image. The description of the second item won't be readable and I'd like to remove "noise" like that. </p>
  
  <p>So how can I remove handwritten regions like that and still maintain a high quality of the printed text beneath? </p>