/proc/empeg_kernel will give you the entire flash space no matter what is currently there. My hijack update script that I grabbed from here does this at the end to compare the two:

echo "Readback kernel.."

/usr/bin/ftp ${IPADDRESS} >/dev/null <<-EOF



        get /proc/empeg_kernel ${TMPFILE}

        quit

        EOF



KSIZE=`/bin/ls -l ${ZIMAGE} | awk '{print $5;exit}'`



echo -n "Comparing ${KSIZE} bytes.. "

dd if=${TMPFILE} bs=${KSIZE} count=1 2>/dev/null | diff ${ZIMAGE} -



if [ "$?" = "0" ]; then

        echo "Success!"

else

        echo "FAILED ($?) -- try again!"

fi

rm -f ${TMPFILE} 2>/dev/null