4. The method defined in claim 1 further wherein extracting one or more features comprises determining a compression type and object location for each of a plurality of objects in the compressed file without decoding any codestream.
4. The method defined in claim 1 further wherein extracting one or more features comprises determining a compression type and object location for each of a plurality of objects in the compressed file without decoding any codestream. 5. The method defined in claim 4 wherein determining the compression type and object location for each of the plurality of objects in the file is based on header data in the file.