Retrieving image from database is easy task. JDBC provides all the necessary API and function to retrieve the image from database. You retrieve image from database and then:
a) Show it to your using servlet
b) Save on your hard disk.
Here is the example http://www.roseindia.net/servlets/retreiveimage.shtml
This example shows you how to retrieve image from database using a servlet and then show it to the user on browser.