I do not watch Google Images all that closely, but there is a guy in the WebmasterWorld forums who said Google images changed how they display the source of the image. I believe what he is saying is that if you use site:domain.com in Google Images, in the past, it would display not just the images hosted on that domain, but all images used on that domain and also show the source of it under it, i.e. like flickr.com and so on.
This is probably best explained using pictures. Let me first show you that a search for site:seroundtable on Google Images only shows images on the web site, but those images can be hotlinked (i.e. sourced) from off the web site:
Google knows it, a similar images command returns the proper source:
Same with Flickr Images for standard searches. It will show the site the image is on but not where it is sourced until you click through:
By the way, that is a picture of me, not Lee Odden.
The original poster described it as follows:
Tonight I noticed a change in the image-search. Until yesterday google shows with the question "site:www.site.com" all pictures that are sourced in that domain.
But now it shows only pictures that link to the domain.
Again, I am not sure if this is new behavior of if am seeing the new behavior or not.
Forum discussion at WebmasterWorld.
Update: Google confirmed this change over the weekend, they said:
Based on feedback from users and webmasters, we have improved the [site:] operator for Google Images. In the past, the [site:] operator filtered based on the image URL, not based on the URL of web pages linking to the images. Now, the operator will run your search over web sites that include images, no matter where the images themselves are hosted, which removes a lot of noise from your results and gives you more control over what you're searching for.
Example searches: [site:digg.com space shuttle], [site:morbidanatomy.blogspot.com], [site:flickr.com/photos/polvero]