100 Million Flickr Images (Yahoo Flickr Creative Commons 100M)

Images and associated metadata from 100 million images uploaded to Flickr under a Creative Commons license

Access Requirements: 
Free; Yahoo and Amazon accounts required; may require current affiliation with research university
Example Publications: 

Wang, Yan, Aker, & Gaizauskas (2014, Proceedings of the 25th International Conference on Computational Linguistics)