A lot of digitally produced images can be easily differentiated from a film based image due to the application of over sharpening. This is easily identified by excessive grain in the image. I have attempted to show a logical progression of an unsharpened image, followed by a sharpened imaged, followed by a sharpened image whose grain has been tamed with AFS GEM (a grain management plug-in for Photoshop.)  Grain management plug-ins, by reducing grain, often appear to reduce the sharpness of an image.

Note that the surfer's face in the final sharpened GEM image actually looks softer than the original unsharpened image.  That's because the original image is kind of blotchy and gives the appearance of sharpness.  Instead, look at the wave and how the final entire image has an appearance of sharpness without appearing blotchy.    

 

Final	Unsharpened
Sharpened	AFS GEM added