Bing / Google / Flickr API: how would you find an image to go through each of the 150,000 Japanese offers?

I am doing a draft of a part of speech and morphological analysis for Japanese sentences. Each offer will have its own web page. To make this page more visual, I want to show one picture that is somehow related to the proposal. For example, for the sentence "私 は 学生 で す" ("I am a student"), the corresponding pictures will be images of a school, a Japanese textbook, students, etc. What I have: tags on parts of speech, for each word. Now my approach: use 2-3 nouns from each sentence and get the first image from the search results using the Bing Images API. Note: all proposal processing up to this point has been done in Java.

You have a couple of questions: 1) which is better (richer body and powerful search), Google Image APIs, Bing Image APIs, Flickr APIs, etc. To search for nouns in Japanese? 2) how do you choose the most important noun from the sentence to perform a query in the image search engine without complex modeling of topics, etc.? Thank!