Here is a quick example of what Geamon was talking about. I took your image added a layer over it and used an airbrush with the following settings to make shadows.
fuzzy circle 19px
scale 5.00
opacity 100.00
mode normal
I use black but a darker gray or a very dark blue would also work.
Click image for larger version. 

Name:	Practicing.jpg 
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Size:	1.63 MB 
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