This plugin adds a reference id field to the database pictures table. When files are uploaded, the field will automatically be set to the configured prefix and the gallery id of the file. Different prefixes can be configured for each user group. Thumbnail display will include the reference_id as a copy-to-clipboard link. The link will be to the image as displayed by the gallery.
Included with the plugin is a reference_id admin tool that can be used to bulk-set a reference ID for pre-existing files as selected in the admin tools.
Update: v1.0.5 small issue correction