A [quick search][1] for "Google images downloader" revealed two possible solutions:

1. [Google Images Downloader][2] - (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][3] - (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.

  [1]: https://www.google.co.uk/search?q=google%20images%20downloader
  [2]: http://download.cnet.com/Google-Image-Downloader/3000-2381_4-75439931.html
  [3]: https://chrome.google.com/webstore/detail/image-downloader/cnpniohnfphhjihaiiggeabnkjhpaldj