Plug-ins and Add-ons for Adding Images to Documents & Slides

http://practicaledtech.com/2018/02/18/plug-ins-and-add-ons-for-adding-images-to-documents-slides/

Pixabay for Google Docs is a free Add-on created by Learn In 60 Seconds.

Pixabay Images Plug-in for Word and PowerPoint

Unsplash photos Add-on

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more on free images in this IMS blog
https://blog.stcloudstate.edu/ims?s=free+images