Identifying field marks of an IBWO and similar birds

Here is an excellent field mark comparison page from David Sibley. It shows various views of the Ivory-bill along with corresponding views of Pileated Woodpecker, Wood Duck, and Red-headed Woodpecker.

Given a fleeting glimpse (and maybe a strong desire to see an Ivory-bill), any of the latter three birds could be the source of mis-IDs.