Import external images/textures in Core Editor

Hello, everyone.
Can you help me with this?
I need to import my own made textures for UI Images, but i can`t find how to do it.

I am also facing the same issue of importing pictures. I thought It was due to the enhancement issue, Then I also enhanced the images via remini online, AI editor. Yet I am also unable to import those files. Let me know if you have got the solution. Thanks