Here's a collection of online photos site links. Many individual sites mentioned have already been posted here, but there are a number of new ones as well. PhotoGraphicLibraries
Most of the sites are free. Some require sign-up. I havn't gone through them all by any means, but the following are several sites on which I've found a number of images likely to be of interest to this forum:
American Memory / US Library of Congress Mary Evans Picture Library (Boer War armoured trains, early tanks and AC's) Getty Images (huge collection) Corbis (huge collection - some overlap with Getty Images) Military Photos (generally more recent photography) Time & Life (mostly WWI, especially note the colour photos of German tanks in North Africa 1943, several photos of Roll Royce/Fordson ACs) Dinodia Photo Library (several photos of WWI armoured vehicles, be sure to click on "international images") New York Public Library Online (early armoured vehicles, also pre WWI catalogues for a number of historic cars and trucks) NARA - US National Archives (Search using the "ARC" link. Unless you plan on visiting them in person, it helps if you limit your searches to items linked to digital copies) Museum of American History (Search using the "SIRIS" link) Imperial War Museum - Collections Online (they've got over 8 million images - you can see quite a few of them online, lots of armoured vehicles) George Eastman House Collection (includes Underwood & Underwood stereoscopic photos of WWI, search engine locates a series of photos rather than individual images - just click on the series title and then you will see individual images) PopperFoto - huge collection, lots of armoured vehicles from Boer War to present, search engine is rather odd (for example a search for "armoured" finds only a few photos while a search for "armour" finds a large number - including many that are clearly labeled "armoured"?!?) Canadian National Archives Photographic Holdings - a good number of photos of early armour as used by the Canadians, be sure to click on the button that limits results to digitized images. Science & Society Picture Library - a few photos of tanks and AC's, lots of trains NewsPlayer- historic newsreel footage including early armour, requires subscription to download videos British Pathe- historic newsreel footage including early armour, low-res videos and stills are free Illustrated London News - historic photos MovieTone - historic newsreels including early armour MirrorPix - large collection of images including early armour ITN Stills - still images from various newreel archives - lots of early armour TopPhoto - early tanks and AC's Images of Empire - some photos of British light tanks & misc
If you run out of fun at these sites, you can also take a look at this page of online photo archive links: Wik
As usual, key words like armor, armour, armoured, tank, gun, artillery, turret, and etc turn up a number of photos. Keep in mind that the search terms associated with each image were likely selected by a photographer rather than someone who really knew what they were looking at, so searching for a specific model of vehicle (for ex. "M1917 armored tractor") might return no hits, when in fact there are several photos of it identified simply as "armoured car" or "tank". The thrill of discovery is part of the fun!