To use music on in a project that will be posted online, you must contact the licensing agency of the record label of the music you wish to use. In addition, royalty fees are required.
However, there are several royalty-free options for using music publicly online. Typically, these websites charge you for their music, but here are two websites that offer FREE royalty-free music that you can post online. But you must credit the source. Credit placement can be at the end of your slideshow/movie/project, as long as it's easy to locate. Here is one:
Credit from this website with, "Music: Kevin MacLeod" If you are using more than one song, please include the title of the song.
Here is our subscription resource for royalty free music. Your user name & password is located in the same place as all of your other database passwords. (if you're not sure what that means email me for the password.)
ANOTHER OPTION for using music:
If you are making a slideshow and want to use music, many of the slideshow makers such as Animoto and Slideroll have music available to use when you create slideshows. So there's no worry about permission or fees. That's already taken care of for you.