Image resource

PIXNIO
One of the first services out there offering large size images.
pixnio.com
Public Domain Archive
The first provider of high quality photos.
publicdomainarchive.com
Public Domain Pictures
The largest collection of images out there.
publicdomainpictures.net
Transparent Textures
The best website backgrounds.
transparenttextures.com
Unsplash
The largest collection of high quality photos there is.
unsplash.com
Wikimedia Commons
A Wikimedia resource that cannot be left out.
commons.wikimedia.org
WPClipart
Great collection of graphics that I cannot say enough good things about.