This guide is based on wikipedia's list of birds of Germany with accidentals removed to keep the guide under 500 entries.
The Grey-headed Woodpecker (Picus canus), also known as the Grey-faced Woodpecker, is a Eurasian member of the woodpecker family Piciformes.
The European Green Woodpecker (Picus viridis) is a member of the woodpecker family Picidae. There are four subspecies and it occurs in most parts of Europe and in western Asia. All have green upperparts, paler yellowish underparts, a red crown and moustachial stripe which has a red centre in males but is all black in females.