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. 
( z1 possible :ARG1 ( z2 use :ARG0 ( z3 you ) :ARG1 ( z4 music :source ( z5 company :name ( z6 name :op "Spotify" ) ) ) :ARG2 ( z7 slideshow :poss z3 ) ) )