This is the documentation of JSU for Jira Cloud. If you are using JSU on Jira Server/Data Center, you can find the documentation here.
The 'Copy / Move Attachments' feature is available from JSU 2.8.0
This post function will copy attachments from/to all related issues.
A user defines which issue should be a source and which a destination.
Any number of attachments can be copied to the related issue/-s.
You have several different options, that define which issue/s will be treated as source/destination for attachments.
Several of JSU's workflow modules provide the option to define the scope of the module on some related issues.
For example instead of copying attachments from one issue to the others you might choose to copy them from all linked issues to the issue in transition (e.g. to group all attachments within one issue)
Conditional copying attachment (controlled by custom field) is checked always only for issue in transition.
Independently if issue in transition is a source or destination.
See the Use Case Copy/Move attachments for a nice example, how several of our customers use it.