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Wikipedia - largely open source
Google Maps - is open source
Vantage article - These 39 Sites Have Amazing Stock Photos You Can Use For Free Vantage blog
The Verge article - The world's largest photo service just made its pictures free to use if you embed the way they want you to.
Getty Search Gateway These open-content ones are free
Met Museum OASC tagged images (Open Access for Scholarly Content) are free
SitePoint - A Collection of 30 Free Stock Photo SitesBoise State Photo Services You can go to their office and search their database of photos. One of their newer options is a Photo Archive. Use password boisestatesocial. If you find a photo in another public gallery where that password doesn’t work email them to get it.
Death to the Stock Photo, for free images (there are tons of other great, free image sources as well)
Free Images - each image has different rights or requirements. 90% or more are truly free images posted by the photographer.
Pablo, for title images and quote images
Canva, for miscellaneous graphics and Pinterest-sized graphics
Skitch, for annotated screenshots
Cloud App, for animated GIFs
Compressor.io, for compressing large images into smaller file sizes
IconFinder and The Noun Project, for icons
Foter is one of the largest stock photo sites