An image says more than a 1000 words.
Allow the content-editor to select one or more options by selecting images.
When configuring a datatype with this editor a set of options can be defined. Options can be added, sorted and deleted. For each option you can set the following fields:
You can also set the minimum and maximum number of options that the content-editor is allowed to select.
The selected option(s) will be stored as a CSV-string (comma separated).
Umbraco 7 and 8 (updated!)