Free Photos

I regularly post my own photos to Flickr under a Creative Commons license. Check them out here.

Otherwise, please check out the below sites, gathered primarily from:
I tried to scrub the list as best I could, but this may contain some errors. Feel free to mix and match with your own.
  1. Air Force
  2. America's Historical Documents - Images and Transcripts
  3. Ancestry Images
  4. Architect of the Capitol Flickr
  5. Army
  6. BigFoto
  7. Biomedical Images from the National Library of Medicine
  8. Bureau of Land Management
  9. Cascades Volcano Observatory
  10. Centers for Disease Control and Prevention Public Health
  11. Central Intelligence Agency Flickr
  12. Coast Guard
  13. CompFight
  14. Consumer Financial Protection Bureau
  15. Creative Commons Image Search
  16. Customs and Border Protection
  17. Death to the Stock Photo
  18. Defense and International Relations
  19. Defense Department
  20. Defense Intelligence Agency
  21. Defense Intelligence Agency Flickr
  22. Defense Video & Imagery Distribution System
  23. Defense Visual Information
  24. DefenseLink (click on Photos/Videos) 
  25. Department of Energy - Photo Galleries
  26. Department of Energy Flickr
  27. Department of the Treasury
  28. DoD Joint Combat Camera Center 
  29. DoD News Photos
  30. Earth as Art
  31. Energy Department's Energy Efficiency and Renewable Energy
  32. Energy Department's Energy Technology Visuals Collection
  33. Environment, Energy, and Agriculture
  34. EveryStockPhoto (choose Advanced Search to restrict licensing)
  35. Federal Bureau of Investigation
  36. Federal Emergency Management Agency Photo Library
  37. Federal Register Flickr
  38. Flags of the World 
  39. Flickr "U.S. Government Works" Search
  40. Flickr Commons
  41. Forestry Images
  42. Free Digital Photos
  43. Free Images
  44. Free Photos Bank
  45. Free Pik
  46. Free Range Stock
  47. FreeFoto (free for non-commercial use)
  49. FreeMediaGoo
  50. Google Image Search (Licensed for Non-Commercial Re-Use)
  51. Government Publishing Office
  52. Gratisography
  53. Homeland Security
  54. IM Free
  55. ImageAfter
  56. ImageBase 
  57. ImageFree
  58. Images from the History of Public Health by the National Library of Medicine
  59. Immigration and Customs Enforcement
  60. Kozzi 
  61. Library of Congress
  62. Life of Pix
  63. Maps (Site with many links to map sources) 
  64. Marines
  65. Money
  66. Morguefile
  67. MorgueFile - photo archive for creatives by creatives
  68. NASA – Great Images
  69. NASA Photos
  70. NASA's Earth Observatory
  71. National Agricultural Library's Special Collections
  72. National Archives Online Catalog
  73. National Cancer Institute
  74. National Center for Complementary and Alternative Medicine
  75. National Cryptological Museum Photos Gallery (Facebook)
  76. National Defense University Govt Photo Links
  77. National Eye Institute images
  78. National Eye Institute's Photo, Image, and Video Catalog
  79. National Gallery of Art Images
  80. National Geospatial Intelligence Agency
  81. National Guard
  82. National Human Genome Research Institute Photo Gallery
  83. National Institute of Allergy and Infectious Diseases
  84. National Institute of Arthritis and Musculoskeletal and Skin Diseases
  85. National Institute of Biomedical Imaging and Bioengineering
  86. National Institute of General Medical Sciences
  87. National Institute of Mental Health
  88. National Institute of Standards and Technology (NIST) Flickr
  89. National Institutes of Health
  90. National Institutes of Health Flickr
  91. National Institutes of Standards and Technology Laboratory Research
  92. National Oceanic and Atmospheric Administration
  93. National Park Service Flickr
  94. National Park Service Historic Photo Collection
  95. National Register of Historic Places Flickr
  96. National Science Foundation
  97. National Science Foundation Flickr
  98. National Security Agency Photo Gallery
  99. National Transportation Safety Board Flickr
  100. Navy
  101. New Old Stock
  102. NIH Image Bank
  103. NIH Photo Gallery
  104. NOAA National Marine Sanctuary Photo Library
  105. NOAA Ocean Explorer Media Gallery
  106. NOAA Ocean Service Photo Library
  107. NOAA's photo library
  108. Nothing but Black Helicopters
  109. Office of the Director of National Intelligence
  110. Office of the Director of National Intelligence Flickr
  111. Official Portrait of the President
  112. OpenPhoto
  113. Peace Corps Digital Library
  114. Penn State's Free Media Library
  115. Pexels
  116. PicFindr (mixture of CC, PD, GNU, etc)
  117. PicJumbo
  118. Pixabay
  119. Pond5 Public Domain Project
  120. Public Domain Pictures
  121. Public Health Image Library from the CDC (Centers for Disease Control & Prevention)
  122. Public image free library
  123. Public Safety and Law
  124. Red Cross photo library
  125. Rgbstock
  126. Royalty Free Icons and Clipart Stock Images
  127. Satellite images 
  128. Secret Service
  129. Smithsonian Images
  130. Snapwire Snaps
  131. Start Up Stock Photos
  132. State Department
  133. State Photo and Multimedia Galleries
  135. Stockvault
  136. SumAll
  137. Superfamous
  138. The National Archives
  139. The National Science Foundation’s Multimedia Gallery
  140. The Public Domain Project 
  141. The U.S. Army Field Band
  142. The White House Flickr
  143. U.S Navy Flickr
  144. U.S. Agency for International Development Flickr
  145. U.S. Air Force Flickr
  146. U.S. Army Flickr
  147. U.S. Army Women’s Museum
  148. U.S. Capitol Photos
  149. U.S. Department Defense
  150. U.S. Department of Agriculture Flickr
  151. U.S. Department of Agriculture Photo Gallery
  152. U.S. Department of Defense Office of Inspector General
  153. U.S. Department of Health & Human Services Flickr
  154. U.S. Department of Housing and Urban Development Flickr
  155. U.S. Department of State Flickr
  156. U.S. Department of Veterans Affairs Flickr 
  157. U.S. Environmental Protection Agency Flickr
  158. U.S. Fish and Wildlife Service
  159. U.S. Geological Survey
  160. U.S. Marine Corps Flickr 
  161. U.S. Mint
  162. U.S. National Archives Flickr
  163. U.S. Nuclear Regulatory Commission Flickr
  164. United Launch Alliance
  165. United Nations News & Media (Photos)
  166. United States Antarctic Program
  167. United States Government Manual Covers
  168. Unsplash
  169. - U.S. States Photo Galleries
  170. Federal Agency Flickr 
  171. USDA Animal and Plant Health Inspection Service Identification Technology Program
  172. USDA APHIS ITP Image Node at Bugwood
  173. USGS Multimedia Gallery
  174. Vecteezy
  175. Vector Scout
  176. WhoIsHostingThis - Free Stock Images
  177. White House Photo Gallery
  178. Wikimedia Commons
  179. World Flag Database 
  180. YouTheDesigner

Public domain. Photo by congerdesign via Pixabay. Updated May 21, 2018.