Revision history [back]

I tried to solve your problem with the idea that you need a method applicable to similar images. So, I wrote a small algorithm that read the pixels of the image and detect when there's a sudden change in intensity(0-255) and blur the subregion. Particularly, I create an imaginary rectangle(1x9 pixel) which I iterate through the image. For each movement of the rectangle I iterate IN it vertically(that is, read 9 vertical pixels) and check for sudden delta in intensity(in this case 30) and blur that area with a normal blur. But before doing all this, I apply a threshold to highlight the hair. The result is not exactly what you asked but hey, I enjoyed myself :-). Here's the code:

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

int main()
{
    Mat image;
    image = imread("hand.jpg", IMREAD_GRAYSCALE);
    if (image.data==NULL)
        cout << "Img not found" << endl;
    namedWindow("hand", WINDOW_AUTOSIZE);
    Mat orig = image.clone();
    threshold(image, image, 180, 255, THRESH_BINARY);

    int height = 8;
    for(int x=0;x<image.cols;x++)
        for (int y = height / 2; y < image.rows - height / 2; y++)
        {
            int whiteToBlack = 0, blackToWhite = 0;
            for (int rectY = y - height / 2; rectY < y + height / 2 - 1; rectY++)
                if (image.at<uchar>(rectY, x) > image.at<uchar>(rectY + 1, x) && image.at<uchar>(rectY, x) - image.at<uchar>(rectY + 1, x) > 30)
                    whiteToBlack++;
                else if (image.at<uchar>(rectY, x) < image.at<uchar>(rectY + 1, x) && image.at<uchar>(rectY + 1, x) - image.at<uchar>(rectY, x) > 30)
                    blackToWhite++;
            if (whiteToBlack > 0 && blackToWhite > 0)
                for (int rectY = y - height / 4; rectY < y + height / 4 - 1; rectY++)
            blur(orig(Rect(x, y - height / 2, 4, height + 1)), orig(Rect(x, y - height / 2, 4, height + 1)),Size(3,3));
        }

    imshow("hand", orig);
    waitKey(0);
}

The result: