This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You could write a servlet that retrieves the image data from the database and resizes it to your desired "thumbnail" size using an imaging library (JAI perhaps?). The servlet would set the appropriate content type headers and return the resized image data as the response. The servlet would be referenced from the html page using the img tag just like any other image.