Above image from National Map Viewer
In this page we will walk through:
1) What available and licensed aerial image data are available to people to use, 2) How to access that data, and 3) What people can and can't do with that data.
Program Managed by the USGS National Geospatial Program (NGP) and "Allows visualization and download of our most current topographic base map data and products for free." The site includes easy download directions.
Images Available: US Topo, Historical Topographic Maps, and Map Indices. --"Available downloadable data themes are: Elevation, Orthoimagery, Land Cover, Hydrography, Geographic Names, Boundaries, Transportation, Structures, while maps include: US Topo and Historical Topo." Link to viewer here.
Restrictions: None specified
Program: This "was coordinated by the USGS as an interagency project to acquire cloud-free aerial photographs at an altitude of 20,000 feet above mean terrain elevation. The photographs were taken with a 6-inch focal length lens at a scale of 1:40,000. Coverage over the conterminous United States includes both black-and-white (BW) and color infrared (CIR) aerial photographs."
Images available: The images in this data set were collected between 1987 and 2007. All the images are available on EarthExplorer
Restrictions Citation and restrictions can be found here: https://lta.cr.usgs.gov/citation