Pic Shadow does just one simple thing - upload a picture and it will add a nice shadow to that image. The default settings generate decent results though you may also tweak the background color, shadow width, etc.
You don’t need Pic Shadow if you have Photoshop or publish pictures via Windows Live Writer because these apps have built-in tools to help you create drop shadows in photographs and screenshot images.
Similarly, most online image editors like Picnik also include support for drop shadow effects but if you are looking for something real quick and simple, consider Pic Shadow.
Related: Create Text Captions with CSS