title: Detect degree of rotation of an image
body: <p>I am doing a project in opencv to detect handwritten characters from a user filled form. I have made algorithm to detect the skew angle of the scanned image using Hough Line Transform. But it does not work when the image is 180 degree rotated since 0 and 180 degree are treated as same by Hough Line function. My image contains some rectangles to fill data in them and some text. So how do i detect if a scanned image is 180 degree rotated or not?</p>
  
  <p>Since I will have to first correct the skew angle of the image then only I can detect exactly where on the image user filled data (which I need to extract) lies using rectangle coordinates from the empty template form provided earlier, answers without using chacater recognition are appreciated.</p>