Google announced when your search has the intent of wanting to see pictures, Google will make sure to show more pictures on the web results.

If you add images, pictures, photos and so on to your search query, Google will likely display a wider array of images directly on the search results page.

One example is a query for [water] vs. [water pictures]:

vs.

Plus, when you mouse over an image, the image pops out like this:

So keep that in mind, if you do get heavy image traffic from Google, the traffic might change.

Forum discussion at WebmasterWorld.