Coding visualize formatting to upload the image file for visual background image

[ShunOtake]

I try to develop the Custom Visual and I want to upload the image file for visual background image.

But I can not understand coding to upload the image file by visualize formatting.
Please tell me the code.

This my code.

setting.ts

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// Background Image
export class BgImageSettings extends FormattingSettingsCard {

public bgImage = new formattingSettings.ImageUpload({
name: "bgImage",
displayName: "Image File",
value: null,
visible: true
});

name: string = "bgCard";
displayName: string = "Background";
analyticsPane: boolean = false;
visible: boolean = true;
slices: Array<FormattingSettingsSlice> = [this.bgImage];
}

------------------------------------------------------------

capabilities.json
------------------------------------------------------------

"objects": {
"bgCard": {
"properties": {
"bgImage": {
"type": {
"text": true
}
}
}
},
------------------------------------------------------------

When I run the Custom Visual and upload the image file,

the charactor type is entered in the variable that contains "visualSettings.bg.bgImage.value".

Please show blow image.