How to create custom backgrounds for custom campaigns AOE2:DE?

ve searched everywhere and can’t find a tutorial. I downloaded the campaign of “The Golden Horde” and reviewed the json files to see how a map was created with the links to the scenarios and only found that in a json file I had the first line: “BackgroundMaterial”: “CampaignBackground04GenghisKhan” bone? can’t we use custom images in the dds format? Or how do I have custom backgrounds and icons?
since the way of carlo in the HD is very different from that of DE. I’d rather appreciate a tutorial