The data field that you associate with your Data Image visualization should contain a URL to an image. The image URL should be accessible to the person viewing your report.

Can't view your image? The number one reason is security. In general, visuals should be publicly accessible, not locked down behind some security mechanism that Power BI can't handle.

Want to see if the viewing problem is Image or caused by something else? Try viewing the image URL in the Power BI Table control, which has basic image viewing support. If you can't view the image in the Table control, the likely reason is related to security or some other issue preventing access to your image.

The visualization is designed to show images from a single data record. If your result set includes more than one data record, only the image from the first record will be shown.

The option to display rounded images works best with images that are square.

If you are publishing your report to PDF or Powerpoint, unfortunately the uncertified version of the visual will not work for you. Vote for vote for this Power BI Idea.