<p>I have a fingerprint image taken from a sliding scanner. However the output does not have clean background. It looks like this:</p>

<p><a href="http://img208.imageshack.us/img208/2622/dirtyie0.png">dirty http://img208.imageshack.us/img208/2622/dirtyie0.png</a></p>

<p>I want to remove the background so that further processing will be more accurate. Something like this:</p>

<p><a href="http://img515.imageshack.us/img515/7530/cleanhh6.png">cleaned http://img515.imageshack.us/img515/7530/cleanhh6.png</a></p>

<p>How to do that? What image processing technique (if any) can be used? Thank you.</p>

To start, I'd increase the contrast to 100% to get a pure black and white image (not greyscale).