I recently finished a 40+ page home-brew realm book covering custom deities and planes of existence. It has many illustrations taken from all manner of online sources including CG hub, Deviant art, the Paizo blog and a few that I drew myself. This book is not for sale!
My concern is the artwork used.
Question: Am I allowed to share this book with the community or does that breach some copy write issues?
-MD
If you intend to make the work freely available I would first ensure that ALL of the artists work is free to use, and acknowledging who/what each artist/work is goes a long way to making the artists happier.
As for pictures from the Paizo blog as far as I am aware all of the images (bar photos) are avaiable for use under the Community Use Policy:
When we say "non-commercial," we mean you cannot sell or otherwise charge anyone for access to content used under this Policy. If you make any commercial use of Paizo Material, your rights under this Policy will be automatically terminated, and any permission granted by this Policy will be immediately revoked.
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(Community Use Policy found HERE).
So as long as you have all work apart from your own clearly credited AND you abide by the intended use of said work AND you aren't charging anyone for any of it then, no, there should not be any copyright issues.