Import json image into Display

Hi there,
I’d like to import an image into display fitting al the echo show 8 frame. With the Basic Display there is a black border all around the image. Is there a way to have the image with no black borders? With the json file I’m having an “invalid” message. Could you please give a look at my json sample and tell me why it is wrong?

{
    "data": {
        "image": {
            "src": "https://example.com/image.jpg",
            "alt": "A cute little kitten"
        }
    }
}

I’ve finally got you have to go on the alexa developer console to get a valid json… But I didn’t read anything in the image documentation. It’s still difficult to manage how to change image display when running on a different block and why there is no image preview on the test mode. Moreover it’s a problem to have a good catch of what are the passages between voiceflow and amazon developer console. The ideal “flow” should be to have everything inside voiceflow to deploy the final skill on Alexa but it seems I have to go back and forth.