It can be done but it's a process :

1) At top of screen hover mouse on "Your Houzz". In the drop down menu click on "Your Idea Books"

2) Find your "Kitchen" idea book and click on it. At top of screen click on the "Edit" button

3) Move mouse cursor to the upper right corner of the pic(s) you wish to move to your "bathroom" idea book (You will know if you are indeed in the upper right hand corner for the mouse cursor changes to a hand symbol). Do a left mouse click

4) Then at top of screen click on "Move Photos too".

thank you so much.... might try in the a.m. after a cup of coffee!! LOL! Thanks again!

P.S. coffee consumed; still cannot find step "2" (once in MY HOUZZ, finding MY idea book).. lol...

@drmuttlee: Just click on any Ideabook you have or want to edit, and you will find the Edit button at the top of the page. Make sure you're doing this on the web, and not the app.