Hi there,

You can add a photo to someone's ideabook only if they have invited you to be a collaborator on that ideabook.

For them to do that, they must go to the ideabook, click the Collaborate button, then add your email or houzz username to the book and grant you editing permissions. Once this is done, the ideabook can be found on your own profile and you can add content to it as well. Hope that helps!