title: How to remove watermark from TIFFs to improve OCR
body: <p>I have a bunch of uncompressed bitonal TIF document images. All of them have a watermark in the middle. When I run them through OCR, the text that overlaps with the watermark does not get recognized. I am trying to see if I can apply some type of cleanup to remove those watermarks to be able to recognize the missing text.</p>
  
  <p>Again, the images are black and white, but when you look at the watermark it appears grey since it has a pattern of black and white pixels that makes the letters in the watermark less "dense" than regular text. At the same time, the watermark letters are very big, much bigger than the regular text.</p>
  
  <p>An example of a somewhat similar image is <a href="http://blogs.zoho.com/image/13000000306068/zoho-writer-watermark-3.png" rel="nofollow">this</a> (except this one is color and the watermark characters in my case are a lot thicker and bigger; my watermarks are also a lot shorter: only 3 to 4 letters long)</p>
  
  <p>It seems that there might be some sort of clean up filter that would be similar to removing large black borders from an image except borders are ually "denser" than a watermark so they appear "more black".</p>
  
  <p>I have 3 tools at my disposal: GIMP, ImageMagick and IrfanView. Can you recommend any specific features of any subset of these tools that might help me?</p>