Classes to encode and decode images
A couple of minor things:


Some people like to always declare what interfaces a class implements, for the sake of clarity. Thus, you could have your subclasses of AbstractImageProcessor also specify implement Runnable.
For consistency, I would rename ImageIOProcessor to AbstractImageIOProcessor.
Not so minor, I would have the method create in ImageProcessorFactory to return an interface, not an abstract class.
While naming is not easy, perhaps you could find a better alternative to ImageIOFileWriter and ImageIOBase64Writer, because they're not only image writers, they also read. They are processors as your other classes.
Do you have any other class extending AbstractImageProcessor besides ImageIOProcessor? If not, maybe you don't need both.