Need advice on background removal of document images taken with a mobile camera

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Hi, I need to implement a mechanism that is able to clean up the image of a "document" taken on a fairly uniform background - such as a top surface of a desk. Also, the document would be surrounded by background on all sides. I am trying to figure out a mechanism by which I can detect the document boundary. I am considering techniques where I can use the knowledge that the document would be surrounded by background on all sides. I'd appreciate any advice - I've tried the following

1. Apply a blurring filter followed by Canny edge detection
2. histogram backprojection

None of them seem to work satisfactorily.

Regards, Kashyap