About the tutorial of finding image using Features2D + Homograph in openCV

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http://docs.opencv.org/doc/tutorials/features2d/feature_homography/feature_homography.html

I download this tutorial source code, and try to play around the the openCV. I use a smile face to test the programme.

And the first testing is a screen shot from my computer:

It success and find the smile face. But the other test is using a real life example like this:

But this time, the smile face can't be detected.

The match result like this:

If I wanna to modify the programme to let it detect the smile face in real life pic. What should I do? Any suggestions? Thanks.