Your lockscreen features a photo gallery that you can easily active following this How to guide.
Copy a folder with pictures to your Huawei internal storage, e.g. photos.
Set your picture source.
Go to Settings > Display & Brightness > More Display Settings > Screen Saver.
Enable the Screen saver.
Select your Picture source, e.g. photos.
Set your playback duration.
Tested on a Huawei P20 smartphone.