JMagick is an open source Java interface of ImageMagick. It is implemented in the form of a thin Java Native Interface (JNI) layer into the ImageMagick API.
Project is now hosted on https://github.com/techblue/jmagick.
Old home page http://www.jmagick.org/ stille has some old binaries that might be usefull.
freeimage4j is a JNIJava wrapper for the superb FreeImage library. Currently not all methods are mapped but loading, saving and simple image manipulation like contrast and brightness are supported. Take a look at the docs for a full list.