Melanerpes erythrocephalus 8½-9½" (21-24 cm)
The only eastern woodpecker with the entire head red (others may have patch of
red). Back solid black, rump white. Large square white pathces are conspicuous on
the wing (making the lower back look white when the bird is at rest). Sexes similar.
Immature is dusky headed; Large white wing patches identify it.
(Source - Peterson Field Guides, Eastern Birds, by Roger Tory Peterson)

Similar species:
 Red-breasted Sapsucker (which does not overlap in range, and has paterned back, yellow belly,  and a different wing pattern). Note the Red-headed  Woodpecker's different position of the white wing patch (especially in flight), white belly, and larger size. It may be confused with the largely dissimilar Red-bellied Woodpecker at times, but attention to the gray face and throat, and barred back and wings of the Red-bellied should eliminate any confusion.