Google Images Search API request restricted?

Question

All! I wanted to develop a feature for a blog I wrote myself. I want to grab the search result of Google Images, and display them in a user-friendly way in or beside my blog's posts editor.

So I did some research on code.google.com

I found Google's official AJAX API for Google images. But on its documentation site it says something like this:

Important: The Google Image Search API has been officially deprecated as of May 26, 2011. It will continue to work as per our deprecation policy, but the number of requests you may make per day may be limited

I know they can restrict the number of requests I can make by my API key.But..

Can anyone tell me how exactly is this API restricted? like how much traffic or requests is allowed?

Is it possible to use this API to develop a Wordpress plugin that everyone else can use?