Gallery Picker Plugin
Overview
The Gallery Picker plugin adds the "imagelink" field type to a document type's editing template. This field type enables authors to select an image from the gallery and reference it within a document.
The Gallery Picker plugin is included by default when you create a project using the archetype.
Screenshots
The Document Type Editor displays the imagelink field type as a Compound Type in the list of available field types:

A document with an imagelink field displays an image preview and provides Select, Open, and Clear actions:

The Image Picker dialog allows users to browse gallery folders and select an image thumbnail:

Source Code
https://github.com/bloomreach/brxm/tree/brxm-14.7.3/gallerypicker