As part of the danish government open data strategy the Danish Geodata Agency offering a WMS free service of their aerial imagery. License (link goes to a danish page)

To use in different OpenStreetMap editors Gregers Petesen have setup a mapproxy.

iD editor URL http://mapproxy.gpweb.dk/tiles/1.0.0/kortforsyningen_ortoforaar/EPSG3857/{z}/{x}/{y}.jpeg

JOSM editor (Note use add TMS)

URL http://mapproxy.gpweb.dk/tiles/1.0.0/kortforsyningen_ortoforaar/EPSG3857/{zoom}/{x}/{y}.jpeg

Potlatch 2 URL http://mapproxy.gpweb.dk/tiles/1.0.0/kortforsyningen_ortoforaar/EPSG3857/$z/$x/$y.jpeg

Coverage and age 100 % coverage of Denmark (43.094 km2) and in 10 cm resolution. Age spring 2012 and some parts of Denmark from spring 2013.

More about the mapproxy setup (text in danish)