You can store your downloads in your account when you signup!
Use this straight forward shot of a black iPhone 6 mockup being held up by an app to showcase your app. Here you can change the background of the mockup. You can pick from 17 different backgrounds to pick on that fits your app. You are also able to bring in a second hand. You can manipulate the second hand to click, zoom in, or zoom out. The iPhone 6 product mockup holds a screen shot of 750x1334px. This is great for any website.
Drag & drop not supported, but you can still upload via this input field: