It looks like twitter could be testing automatic in-stream image viewing on some users timelines. The Next Web noticed that users are starting to see images on their feed without having to click on them. The new in-stream image preview would cut down on the continuous clicking and would view all photo thumbnails easily. Twitter has yet to announce any changes to the timeline. Check out the photo in the gallery.
Yeah we noticed that too. Makes sense since it makes it more seamless with less clicking.