Is it copyright infringement to show a list of search results along with a thumbnail taken from the corresponding image from google images for that word? Bearing in mind that the images could be from any site whatsoever?
INAL and really, you should speak to one to get a solid answer on this.
That said, can you explain a little more about how you intend to use these images? There's a big differance between using them as thumbnails for your own site/content and buiding an image search tool along the lines of Google's Image Search.