We rely on the “used by” field of all of our assets to help us determine if it’s OK to delete an asset without it affecting any dependent assets. We also use this information should we need to change that asset (and allow to understand which dependent assets need to be re-reviewed). But I just noticed that the “USED BY” information always displays as “NONE” for images:
This specific image is used in the “curved paper with sidebar” email template that we use for all of our real-time email alerts. Is this issue happening within your Marketo instances?