```bash
REMOTE_DIR="/sdcard/DCIM/100MZLLA/"
adb push...
for i in `seq -f '%04g' 2 $1` ; do
  FILENAME=IMG_$i.jpg
  adb shell "cat ${REMOTE_DIR}/IMG_0001.jpg > ${REMOTE_DIR}/${FILENAME}"
done
```

I understand you need the first `if` to do the optimization of not copying several times the same file.