Both Lulu and kdp have covermakers as well as publishing
Lulu
https://www.lulu.com/
Kindle direct Publishing
https://kdp.amazon.com/en_US/
Canva
https://www.canva.com/
free place to make book covers with royalty-free pictures
bit like Photoshop with pictures
need to sign up to keep old work but it's free to use
Edit.org-online editor
https://edit.org/
you can make covers with images found there too like Canva.
UnSplash
https://unsplash.com/
another free royalty-free picture place
Gimp
https://www.gimp.org/ this can help make covers and resize cover too and it's a free it is an alterinative to Photoshop.
Photoshop
also good for making book covers just costs to use.
Photoshop alternative comparison
site I've only tried Canva and Gimp know they good
Covervault
Not actually publishing a book but it is a useful site with useful mockups you can turn his mockups into you book with a little skill and Photoshop.
https://covervault.com/
