How To: Use Google Drive photos in ArcGIS Online pop-ups
Images can be included in ArcGIS Online pop-ups by entering a direct image URL. These images can be hosted on ArcGIS Online or an external website, such as Google Drive and Flickr. The URL to be used in pop-up configuration must be the direct image URL. However, this URL is not given directly by Google Drive.
To get direct image url on Google Drive:
Click the image on Google Drive.
Click the Share button at the top of the page.
Click Sharing settings.
Click Advanced in the bottom right corner of the sharing box.
Click Change....under Who has access.
Choose On - Public on the web and click Save.
Before closing the sharing box, copy the document ID from the URL in the field below Link to share. This URL contains the image id. For example: https://drive.google.com/file/d/0B14bzGsfJ06JMDF5Y2VsNU9FRVk/view?usp=sharing
Replace <image_id> in this URL with your image id: https://drive.google.com/uc?export=view&id=<image_id>
This is the URL to be used in pop-up media configuration.