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.

Comments:
Nuttakorn
06/09/2011 09:09 am
Now when you search on web search like "Singapore picture", it shows like this http://yfrog.com/73n3wp same as video.
SocialNetGeek
06/14/2011 08:05 pm
Dude. This feature totally sucks now. It's not showing relevant images at all. The old one was better.