Ever, since Twitter was release, sharing photos via the micro-blogging service was one of the most important and used features but it took Twitter a little bit longer to realize it by introducing its own photo and picture hosting which is now alive for roughly two years. And indeed, within my timeline this feature is heavily used but so far, you only knew that the tweet contained a photo by the respective URL, within the tweet (for instance pic.twitter.com/xyz) and only opening the tweet showed the respective picture; doesn't matter if on the web, Twitter's original Android, iOS or Windows Phone apps. However, yesterday evening my timeline on one of my Android devices showed me the picture preview straight within the timeline, without opening the respective tweet.
On the left, the well known timeline with indication of photos (by URL and Twitter Card icon); on the right the same timeline now showing a preview of the picture, right within the timeline.
Interesting enough, when immediately verified on a second Android phone with the same Twitter client installed, the pictures weren't shown in the timeline. Also, this feature appeared only for a couple of minutes and went a little bit later. However, later in the evening the same behavior appeared again but since then, I haven't seen it anymore.
At this point, it's not clear if Twitter is testing a new feature or if it was a misconfiguration on Twitters side. At the end of the day, the timeline preview isn't new at all, it's already available for a couple of 3rd party Twitter apps, mainly on Windows and Mac OS, but it's definitely new for Twitter and even more on mobile devices.
Overall, previews within the timeline wouldn't be bad at all, since it reduces the clicks, on the other hand is the screen estate on smartphones limited and the whole timeline became much more noisy.
I reached out to Twitter for a statement, let's see what they have to tell us.
Cheers ~ Arne