I'm using something like the following piece of code:
<code>File source = new File("C;\test.png");
File dest = new File("C:\test_thumb.png");
BufferedImage buffered = ImageIO.read(source);
Thumbnails.of(source).forceSize(150, 150).toFile(dest);</code>
This is being run as part of an app running on Tomcat.  The thumbnail is 
created successfully but it appears to be locked in some way.  Although Windows 
will show me a thumbnail of the image, when I try to open the file in a variety 
of programs then the image is unreadable.  If I stop Tomcat, then the file 
becomes readable.
It appears that something is keeping some form of lock open on the file.  If I 
get a chance, I'll dive into the code and see if I can spot what.
This is on Windows, Java 1.6 & using Thumbnailator 0.3.7 (latest at the time of 
writing).