When you use an image, a video or a music that doesn’t belong to you, make sure that that it is free to use (no copyrights) and that you are allowed to use it for commercial purpose.
In some case, the owner will simply ask you to credit his·her name on your page.
In other cases, you will have to pay a fee to use the creation.
We recommend to always use multimedia elements you have made or that have been created specifically for you.