Words are 'gold' when doing image searches since using the right ones can get you results in instant, but you don't always know what to type. Sorting can help in these situations since it narrows down the results, thus helping pin-point the content desired.
In that note, that sorting is good, Google has went on and added the ability to 'sort by subject' when doing image searches. Available in the left side column, under 'Sort by relevance', sorting by subject will split the results page in multiple lines, each one focusing on a specific item. Take the image below, the search was for 'london', so the subject-sorted results depict the major landmark found in the UK capital.
"Sorting by subject uses algorithms that identify relationships among images found on the web and presents those images in visual groups, expanding on the technology developed for Google Similar Images and Google Image Swirl," said Donald Tanguay of the Google Images team. "By looking at multiple sources of similarities, such as pixel values and semantic relationships, and by mining massive amounts of data, we can make meaningful connections and groupings among images."
Sort by subject is already rolling out and should be available globally within a week or so.

Source : tcmagazine.com