TreesOfNorthAmerica.net and CirrusImage.com offer extensive alphabetical lists of North American tree species with links to more information and photos of each species. TreeNames.net provides information and photos of tree species from all over the world.
TreesOfNorthAmerica.net, CirrusImage.com, and TreeNames.net all require knowledge of the tree species in order to view the appropriate photo. To identify a tree, use the tree identification key at DiscoverLife.org. Tree identification relies mostly on leaf type, shape, margin and arrangement, plus additional information such as any fruits or nuts on the tree.
Identifying trees in winter is more difficult, as it relies on bark features and branching patterns. TreeBarkID.com provides questions and photos that can help in winter tree identification.