Copyrights tab allows you to set the copyright text and watermark image that will be shown on the map window in Earthlight.
This is how the copyrights text is displayed in Earthlight:
This is how Earthlight look with a watermark image set:
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To set a watermark image you have to use a Polygon Style resource. To learn how to prepare a watermark image please visit: http://statmap.co.uk/?page_id=6257Earthlight watermark image