First, when taking a Live Photo in step 6, hold your iPhone in landscape orientation, with its Home button on the right. There are two stumbling blocks to be aware of. Note that the crossfade and enlargement from a Live Photo's still part to its video is baked into iOS and can't be suppressed, but perhaps you've realised this already with Live Photos made using your iPhone's camera. This opens up all sorts of opportunities to turn hand-drawn or computer-generated animations into Lock screen wallpapers, or you may just want to convert an animated GIF of amusing animal antics for when you need a pick-me-up just press your phone's screen and try not to burst out laughing if you're somewhere that would be inappropriate! Obstacles to watch out for (If you prefer, you can use another app that can export QuickTime movies in Keynote's place.) It turns out that it's possible using nothing more than Keynote, Photos and a shared photo album published to iCloud. The ability to use a Live Photo as the Lock screen wallpaper on an iPhone 6S or iPhone 6S Plus is ripe for fun, yet Apple provides no way to use an existing video in this way.

Live photo lock screen