How to crop biggest rectangle out of an image

Question

I have a few images of pages on a table. I would like to crop the pages out of the image. Generally, the page will be the biggest rectangle in the image, however, all four s

Answer 1

That's a pretty complicated task which cannot be solved by simply searching contours. The Economist cover for example only shows 1 edge of the magazine which splits the image in half. How should your computer know which one is the magazine and which one is the table? So you have to add much more intelligence to your program.

You might look for lines in your image. Hough transform for example. Then find sets of more or less parallel or orthogonal lines, lines of a certain length... Find prints by checking for typical print colours or colours that you usually don't find on a table. Search for high contrast frequencies as created by printed texts... Imagine how you as a human recognize a printed paper...

All in all this is a too broad question for StackOverflow. Try to break it down into smaller sub-problems, try to solve them and if you hit a wall, come back here.