As well as icons, the Noun Project now has Creative Commons licensed images. You can download the basic version of the image for free - Noncommercial use allowed, social media quality, no crop/edit allowed, must attribute artist. Registration required.
CSIRO has provided permission for anyone to freely use, repost and transform the collection’s 4000+ high definition images and videos. The library represents more than six decades worth of environmental, industrial, agricultural and technological research images.
Includes forestry, IPM (Integrated pest management), insect and weed images with identification, taxonomy and descriptions. Images made under Creative Commons Licence for use in educational applications.
Includes biomedical, healthcare, and social history images. Images are available under one of two Creative Commons licences - either free use for any purpose or free use for non-commercial purposes only.