#!/bin/bash

for image in "@" ; do
  while true; do
    timestamp="$(shuf -i 1400000000000-1469999999999 -n 1)"
    extension=${image##*.}
    filename="$timestamp.$extension"
    [[ ! -f "$filename" ]] && break
  done
  mv "$image" "$filename"
done

./randomizeImage.sh image1.jpg image2.jpg