Background of Request

Confluence 5.7 introduce a new feature where it is able to preview attachments as can be seen here. One of the feature available is to covert a thumbnail of attachment into a link with "Show as link" button.

However, once the attachment is converted into a link it is not possible to convert it back to thumbnail. This is because "Show as Thumbnail" button is not available for "Linking" even if it is a link of an attachment.

Possible Implementation

Confluence "Linking" feature should be able to differentiate attachment link and URL link. From there, Confluence able to provide "Show as thumbnail" button only for attachment link.