If you are eager to test out the new image handling, check out the new beta for OS X . I have made this an opt in only feature for now. To get inline image support, go to preferences -> display and check the option for inline images. While you are testing this, try out drag and drop to the text field and markup (the little arrow in the upper right of the image when you attach it). Clicking an image in chat will bring up preview and you can use the export button to send that image anywhere you want. Animated gifs are not animated in the thread (yet) but will be when you click them.
I had a few spare minutes today, so I decided to finish support for inline images in chat in the OS X client. Most of this will come to the iOS client as well. It does not yet support the privacy setting to disable checking the HTTP head of every link to identify an image but beyond that it is mostly done. I also added support to OS X’s quick look as well as markup for images that can now be dragged into the text field before uploading.