Available books identifying trees by picture include 'The National Audubon Society Field Guide to North American Trees,' 'Trees of North America: A Guide to Field Identification,' 'The Tree Identification Book' and 'Identifying Trees.' Each title is readily available through suppliers such as Barnes and Noble and Amazon.
LeafSnap.com is an online photo field identification guide developed by researchers from Columbia University, the University of Maryland and the Smithsonian Institute. A free mobile app available from Leaf Snap uses visual recognition software to help identify tree species by photographs of leaves. The Peterson Field Guide series pocket-sized books are convenient to carry and include detailed color illustrations.