Flickr service is probably the most popular photo sharing website. You can download, comment and share images. Always keep in mind that not all images can be modified or used for commercial purposes and that some require a reference to the source and author.
Freepik offers more than 1.3 million images, photographs and artwork free to download. Take care however, not all the downloaded images can be used for commercial purposes.
Designpacks is a good place to find good images for the header of a web. The images are grouped into catalogs that can be downloaded in .zip format.
Fotolia is one of the best sources of professional images. You’ll find photos and artwork created by talented designers from 0.75 €.
What are your sources for free images? Share them with us. :)