Image not of any known type, or corruptDeclared imageMIME Type:’ image/webp
Cesium for Unreal does not yet support WebP images. Keep an eye on this issue:
ty 
If I want to load , I have to change the image type? Or is there any good way? 
You can change the image type, add WebP support yourself (pull request welcome!), or wait for us to do so. Sorry, there’s no workaround. If your tileset was generated by Cesium ion, there’s a checkbox in the UI to use WebP, you just need to uncheck it.
ok ty