From time to time we are receiving request about ability to add attachments to Scheduled Issues, we do not support this field for some reasons. On of them is that it's really risky to manage some data storage place where we would need to store attachments for the future usage. It's risky because we're not instance administrators and we cannot guarantee that attachments will live there and be available whenever they will be needed while creating an issue.
Here are few ideas that might help you to use attachment or attachments in scheduled issues.
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https://bitbucket.org/apdc/the-scheduler/issues/320/add-ability-to-attach-files-from-scheduled
https://bitbucket.org/apdc/the-scheduler/issues/304/sugesstion-add-images-on-schedule-task-to
https://bitbucket.org/apdc/the-scheduler/issues/171/pictures-in-schedulded-issues-not
https://bitbucket.org/apdc/the-scheduler/issues/23/add-attachments-to-scheduled-issues