How to create a musical slideshow with iphoto<br>Choose the photos you want to show during your video. Choose your music; make sure whatever song you choose is not drm protected. You can use songs you have bought from the itunes store, and you should not use any song that you do not have express permission to use.
You can use music from Spotify for your slideshow 
The statement suggest that you use music from itunes for the slideshow but doesn't say that you have to. It is possible that you can choose music from another source such as spotify but it isn't confirmed. 
( z0 possible :ARG1 ( z1 use :ARG0 ( z2 you ) :ARG1 ( z3 music :source ( z4 company :name ( z5 name :op "Spotify" ) ) ) :ARG2 ( z6 slideshow :poss z2 ) ) )
(z0 / possible-01
    :ARG1 (z1 / use-01
              :ARG0 (z2 / you)
              :ARG1 (z3 / music
                        :source (z4 / company
                                    :name (z5 / name
                                              :op1 "Spotify")))
              :ARG2 (z6 / slideshow
                        :poss z2)))
You can use music from Spotify for your slideshow
z0 :ARG1 z1
z1 :ARG0 z2
z1 :ARG1 z3
z3 :source z4
z4 :name z5
z5 :op1 0
z1 :ARG2 z6
z6 :poss z2