If you want to add emphasis to an image in a Word document, you don't need a special piece of software or app to edit it — you can use a tool that's built right into Word.
Here's a Word document "sampler" showing different ways I modified one image to create different effects:
Watch this 30-second video to see how you can do it too:
The above video is from Microsoft's Word 2010 Tips and Tricks Tip #5: Crop a Picture to a Shape.
Image of George Washington source: Wikimedia Commons