How to use no-asset file in plugin content after packaging project.

I have a plugin which uses some png files for slate style. I put these files in the plugin content directory and I make sure the config “CanContainContent” in the uplugin file is set to true. And I find this config just affects uasset files in plugin folder. So I wonder how to automatically packge those no-asset files in the plugin content to paks files. Thanks to any help.

ps:
Slate in engine content directory exists in “MyProject-WindowsNoEditor.pak” file and also in the “PackageDir\WindowsNoEditor\Engine\Content” directory. Is this necessary?