Google says they’re rolling out the new feature today, although it doesn’t appear to be available to all users just yet, so if you don’t see the new filter option, be patient for a little while. The new filter not only shows just animated GIFs, but it allows users to preview the animated GIFs directly from the results page.

Animated GIFs have already been included in Google Image Search results, but searchers haven’t been able to search for them specifically until now, and users were never able to preview them in action from the results page, so the new filter should definitely make it easier to search for that animated GIF you’ve been looking for.

GIF previews in Google Image Search have existed for at least a month.

Being able to filter by animated GIF should be useful. Will see.

I've been using Google Image search on animated gifs to try to find provenance for some material with some success. They seemed to have been doing a pretty good job of capturing a relevant image of an animated gif, thought not the full course.  

Finding an animated gif using an image would be useful too. Previewing them, even more!

I agree with you Greg -- they're good but not great for that kind of thing.

I wouldn't trust them for provenance in some cases, but they're better than nothing at all.