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A quick search for "Google images downloader" revealed two possible solutions:

1) Google Images Downloader - (Desktop application)

Google Image Downloader (GiD) allows you to download images by entering a search term. It then hits the internet and downloads the full sized images from all of the sites Google images returns.

Read more: Google Image Downloader - Free download and software reviews - CNET Download.com http://download.cnet.com/Google-Image-Downloader/3000-2381_4-75439931.html#ixzz2xAqVnmTR

2) Image Downloader - (Chrome extension)

See all images shown or linked on a web page and download them.

I guess if you want this kind of functionality in your own app these would be a good starting point.