With every major Android upgrade, Google brings new emojis, and with Android O, it's not changing as well. Google added new emojis with the Developer Preview of Android O, and they look a lot better than the blob styled ones seen on the Android N.
Finally, Google is ditching the blob emojis, which was hated by many out there and replacing them with much-rounded emojis and they look decent. That said, the new emojis is available only for the Android O users right now.
However, folks at xdadevelopers managed to port the emojis to other Android OS versions as well. Do make a note that your Android device should run on Android 5.0 Lollipop and above for the emojis to support.
Head over to this XDA thread to download and install the Android O emojis on your Android smartphone right away.