In previous years I’ve covered sites that provide free legal images for use in site design. 2016 is no exception, with several more significant photo / illustration sites coming to my attention. One important criteria for inclusion on this list was ease-of-use: many have integrated search, and none require a login or registration.
Superfamous

A small but beautiful collection of photographs - mostly landscapes, nature, architecture and abstracts, often in square aspect ratio - by Folkert Gorter, provided under a Creative Commons 3.0 Attribution license. (His Open Foundry collection of free fonts is very much worthwhile checking out too).
StreetWill

StreetWill provides user-submitted photos under the increasingly popular Creative Commons Zero license, which allows you to do whatever you want to the images, including commercial uses, without any cost or requirement to credit the creator.
Cupcake

Cupcake provides photographs by Jonas Wimmerström, also licensed under CC0. Other photographs are also available on his store, for a price.
tookapic

While tookapic offers most of its wares at a simple $10-per-photo royalty-free conditions, reader Sergio Roldan pointed out that it has a somewhat-hidden free filter, linked to here, provides images that are completely gratis.
U.S. Government Image Search

As previously mentioned, most government agencies are obligated, by law, to make any work they produce freely available to the public, which has already paid for the work through taxes. This search site allows users to search available US government image archives, including such diverse resources as the Flickr account of the NASA Goddard Space Centre, the social media accounts of the US Nation Parks Service, and the Instagram account for the US Marine Corps.
UHDWallpapers

Provides wallpapers in UHD (4K) resolution, under Creative Commons. While they are intended for use on personal desktops, the images have more than enough resolution and public domain licensing to allow them to be used on your site.
StockPic

StockPic takes the very popular approach of bundling images into weekly eMails, allowing individual images to be downloaded from the site. Images on the site are lightly watermarked, but downloaded artifact-free at a good resolution. Stockpic uses its own license that offers the images free for commercial use, with no requirement for attribution (although credit is always appreciated); the only restriction is that the images cannot be redistributed.
KaboomPics

Offers eMail subscription and site downloads of individual images. KaboomPics features mostly interiors, food, and closeups.
PixaBay

PixaBay supplies nearly 600,000 free photos, vector images and art illustrations, under a CC0 license. Low and medium resolution images are available for download with a captchca test; high resolution images require (free) registration. Pixabay also offers the best search options of all the services shown here, with filter options for color, orientation, and resolution.
SplitShire

Many images offered free for commercial use, without copyright. SplitShire does not offer direct search, but images are sortable by tags. Grouped images can be downloaded at a low cost.
Life Of Pix

Free high-resolution photos provided by the Leeroy advertising agency in Montreal, free for personal and commercial use. Like PixaBays, Life of Pix also offers videos via a related service, Life Of Vids.
Norebbo

The last site in the list is rather unusual: Norebbo is the blog of an illustrator who provides lo-res versions of much of his work away for free; high DPI versions can be purchased from his store.
Photograph by Hiroki Akao, courtesy of tookapic.
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