Images

• Creative Commons search engine that indexes over 300M CC-licensed images.
• Flickr Commons. An attempt to catalog the world's public photo archives.
• https://public.work - search engine of public domain images, via kottke.org and @holly_cummins@hachyderm.io.
• Openverse - search engine for openly licensed images, audio and more
• Unsplash. Fair warning, has started watermarking some photos.
• Pexels. Free-to-use (without attribution) stock photos, images and videos.
• Lexica - Stable Diffusion search engine. Search for images generated by the Stable Diffusion AI text-to-image model.

In related news

• https://www.flickr.org
• https://pechaflickr.net
• Google broke its image search. And hey CogDog, thanks for posting!
• https://cogdogblog.com/2022/12/flickr-fdn-thanks/

Text

• https://crowdview.ai - search engine that exclusively searches discussion forums

Scientific

• https://www.scienceopen.com/search (blog post)
• https://search.crossref.org
• https://scholia.toolforge.org (very cool - relies on WikiData, hosted on WikiMedia Toolforge)