You would expect the image results that show up in google’s universal search to be the same as they are in google’s image search, but there is a clear difference between the image results in universal search and in image search. Most of the times the first X amount of images from google image search will show up exactly the same for the same search phrase in universale search, but not always. Even when it is the images look the same they are not always realy the same. Below you see screendumps of the search results for “Jack Herer” in universal search and in image search.
Universal search: http://www.google.com/search?q=jack+herer
Image search: http://images.google.com/images?q=jack%20herer
It looks like exactly the same image results are displayed in both searches, but if you look more closely you will find out this is not the case.
My theory is that in universal search the context in which the image is displayed needs to be textual content on the subject as the filename & alt tag of the image suggest the image is about. In image search you seem to get more results from image galleries and pages that contain several images.