http://www.istockphoto.com/ by http://www.gettyimages.com/
https://www.shutterstock.com/ or their limited version https://www.bigstockphoto.com/
https://stock.adobe.com or their other one at https://www.fotolia.com
https://photodune.net/ that is part of the Envato Market : https://market.envato.com/
https://www.pexels.com/ – All images are distributed under the Creative Commons Zero CC0 License, which means that you can do whatever you want with them, including commercial use – resizing, cropping .. whatever.
https://www.pixabay.com/ – Another good one, using the same CC0 license. They claim to contain about 850.000 images already, which makes them a bigger source than pexels.com.
https://www.unsplash.com – Community of photographers who share their work under CC0 license too, this one is good for more artistic work. You can also browse by author, check how many downloads a photo has etc …
http://www.gratisography.com/ – This one features content from just one photographer, so the collection is limited … but the quality is awesome. Great for content with a bit of personality.
https:/www.picjumbo.com/ – This is a one man show too, the images are shared for free with only one limit – redistribution.
http://freestocks.org/ – This one utilizes full CC0 license again, there are some great photos from several authors to download.
http://www.lifeofpix.com/ – Not the biggest one, but using CC0 again and offering solid selection of HQ images. I can see these working well on blogs, sites …
https://stocksnap.io/ – Another license free – they will even send you the most popular images to your email.
http://deathtothestockphoto.com/ – And one more, again with almost no limitations other than non-pornographic or defamatory use … many of these sites require this actually.
http://openphoto.net/– On this one, the license can vary from one image to the next, it’s always written under the image thou, so easy to find.
http://www.publicdomainpictures.net/ – Quite a big one here again, almost 200.000 pics, some with additional licensing, but many are distributed as public domain.
https://www.splitshire.com/ – Free to use with some content limitations.
http://www.1millionfreepictures.com/ – The author doesn’t really offer a million of photos, but there are many to choose from. Mass download available at an extra price.
http://viintage.com/ – This is a special one, offering vintage style graphics and 1000s of them with any limitations. Premium stuff available too.
http://nos.twnsnd.co/ – This one also offers old photos, free of copyrights.
http://publicdomainarchive.com/ – Not sure how big this one is, but it’s free of copyrights too
http://skitterphoto.com/ – Another one built on user submitted content under the CC0 license.
https://morguefile.com/ – Close to 400.000 images on this one again. Quality varies based on the author. Free to use for commercial projects too.
https://freeimages.red/ – Quite a small one again, but with CC0 license, so worth a look.
https://www.goodfreephotos.com/ – And yet another one with public domain photos, 16.000 to choose from.
http://realisticshots.com/ – Great one for social media posts or blogs, limited amount of pics but very good quality.
http://freenaturestock.com/ – Need some nature shots? Smaller collection from one author, but with a free license
http://magdeleine.co/license/cc0/ – This site has photos with several licenses, I linked directly to the CC0 section.
http://isorepublic.com/ – This will be the last one for today. Very open license again, no attribution needed, thou they have some limitations as per their terms.
如果你对 Creative Commons licensing还不太了解，可以看这里： Creative Commons licensing