What is a contour in OpenCV?
Contours are defined as the line joining all the points along the boundary of an image that are having the same intensity. Contours come handy in shape analysis, finding the size of the object of interest, and object detection. OpenCV has findContour() function that helps in extracting the contours from the image.
How does OpenCV contour detection work?
To put in simple words findContours detects change in the image color and marks it as contour. As an example, the image of number written on paper the number would be detected as contour. The part that you want to detect should be white like above numbers in 1st image.