Simple image processing

I have 2-d simple images like a rectangle triangle etc. in bmp files. Each bmp image contains one geomtric shape and nothing else. (white background) Images are all enclosing shapes. Pen width of the images are 1 or more pixels. I need a code in C# that takes an image and traces its outer borders, and returns an image which only consists of this border. It is basically simplified version of contour following. Accuracy is very important; returning image must still be an enclosing image and no pixel on the border should be missing. C# or C++ library that I can call from my C# code is a must. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform .Net, C#, C++