It seemed to me that the answer would lie in the corrugations of the cardboard, so...
I put the image into a 'technical' image processing program that allows one to build custom convolutions (filters). After boosting the contrast, I applied a 80% 5X5 LaPlacian convolution, followed by a narrow-spatial shadowing filter in the axis of the sunlight direction. This made the corrugations stand out very sharply.
You are right: the corrugations do not appear to be distorted appreciably by pencil pressure. Furthermore, the corrugations do extend into the "shadow" cast by the boy's hand.
This, and the fact that the corrrugation shadows appear to match the incident light angle, makes it unlikely that a photo of another piece of lettered cardboard was 'pasted' in atop the original. And it is certain that the image was not "cut in" around the hand shadow, as suggested earlier.
Of course, the "shadow" (whose outline looks suspect to me) could have been (using transpqrency) added with a simple editor like Photoshop.
However, my opinion is that the entire photo is a posed fake.