In this GIMP tutorial on image manipulation I’ll teach you how to tear up a photo in GIMP simply by using selections and layers in GIMP. The distress selection filter is used so you can get a realistic torn up photo effect.
Using the apply canvas filter and drop shadow in GIMP will let you know how to give it a professional look.
Sunflower photo:
http://www.burningwell.org/gallery2/v/textures/plants/Flowers/TT7040108.JPG.html?g2_imageViewsIndex=1