To generate search assist image results, go to Yahoo Image Search and begin typing. If the query is popular enough and can be refined, Yahoo will show images within a different refinement category. So in the example above, the first image on the left, is a refinement option to see [barack obama family] pictures.
In addition, after you search, you can click on the little up arrow under the search box, to open up Search Assist. This feature, i.e. opening the search assist box after a search, is new.
Yahoo also said they will be launching Search Assist for Images on Yahoo.com soon.