So in other words you need to have used the compressor to compress what you are copyrighting, and that which you used it on must have been physically stored in its entirety. Is it provable that this all occurred, if there's no requirement to still have the original? It would require that you also supply the compressor to the court, so that somebody can use your self-extracting magic decompressor, recompress the result, and end up back in the same place. But you could make your compressor simply emit your decompressor, ignoring the input!