I can see that a lot of Chrome Extensions have a promotional image in the list. For example with gmail : https://chrome.google.com/webstore/search-extensions/gmail?hl=fr&utm_source=chrome-ntp-launcher
I don't find where to set this image in the Developer Dashboard. How to ?
Visit the developer dashboard and click on the Edit link.
Scroll down (below the screenshots section), and upload the images for your extension:
The images will be put in the review queue after uploading it. If the images meet the criteria for promotional images, it will show up in the Web store within a few days.
You won't get any notifications when the images get (dis)approved. Send a message to cws-assets@google.com to query the status of your images. And no, you can't see the status at the dashboard, contrary to what the official documentation states.
来源：https://stackoverflow.com/questions/15855373/how-to-set-a-promotional-image-in-the-chrome-extensions-list