example => python image_downloader.py --url "http://www.image-net.org/api/text/imagenet.synset.geturls?wnid=n03791053" --count 1000 --save_dir scooter
example => python image_downloader.py --url "http://www.image-net.org/api/text/imagenet.synset.geturls?wnid=n03791053" --count 1000 --save_dir scooter