AWS ECR Storage Usage

In the AWS Cost Explorer, by filtering on service: Amazon ECR and applying a group by usage type, you could get down to an hourly pricing per region for your repositories. From there, you could get a rough estimate of the total storage by using the pricing of the ECR storage for that region.

If you need something more precise, I suggest to look at the Cost and Usage Report (CUR), it will have more granular details per repositories, etc. Using Athena it's possible to build query to get the exact report you're looking for.

Here's a link to the documentation to use Amazon Athena to query CUR : https://docs.aws.amazon.com/cur/latest/userguide/cur-query-athena.html