These mockups are %100 free and %100 public domain. No need to worry about copyright or anything.
Each mock up is made from scratch in Adobe Photoshop CC. Already familiar with using Smart Objects? Great! If not, it's super easy. All you have to do is insert your own artwork into the Smart Object layer, save, and your mockup is ready to go.
If you'd like to give back, I have included a link to my PayPal page (below), where you may donate any amount you like. Donations are greatly appreciated, and go towards developing more free-to-use design tools, like these.