Openverse (stored in the plugin as creative-commons / cc_search) returns Creative Commons images from many providers (Flickr, Wikimedia and others). No API key is required.
You can also browse the same catalogue manually on Openverse (WordPress).
Free. Available on the Free plan.
Source badge: Photos.
Gutenberg: yes. Enable it as a search tab on Magic Post Thumbnail → Gutenberg Block. API keys and filters stay on Source.
Open the bank in Source #
In version 7, banks are configured from Magic Post Thumbnail → Source. Click the bank in the left column (or tick it to add it to the chain), then click Configure. The Banks Settings panel opens on the right. Save when you are done.
The left column is the Automatic generation chain used by the editor button, bulk generation, cron and imports. Drag to set priority: the first bank is tried first. Unchecked banks sit below the chain.

Options #
- Source
- All sources
- All except flickr
- Other
- Rights — optional license filters (cumulative). Choosing them can reduce relevance but helps restrict results to free-to-use images:
- Zéro (CC0)
- Attribution-NoDerivs
- Attribution-NonCommercial
- Attribution-NonCommercial-ShareAlike
- Attribution-NonCommercial-NoDerivs
- Attribution-ShareAlike
- Attribution
- Public Domain Mark
Leave them unchecked to search every licence Openverse returns.
- Image Type — Default, Illustration, Photography, Digitized Artwork.
- Aspect Ratio — Tall, Wide, Square (default: Tall).