Now you can reply with a photo or video to specific photos, videos, and reshared posts in Direct. Your reply will automatically include a sticker of what you’re replying to. Just hit “reply” to open the camera, take a selfie, and send.
There's also the option to send a split-screen reply. You can do this by tapping on the sticker. "Add your own perspective by drawing on the sticker, whether you’re painting a mustache on your friend’s selfie or doodling on a beach photo."
You can download Instagram from the App Store for free.