You can store your downloads in your account when you signup!
Place your start-up product screenshot into this office environment. The large landscape 1440 x 900 px mockup stage in this Macbook allows for highly detailed viewing. To the left of the Macbook lays a black iPad with screen on and icons up. To the right is a green, glass lamp. The reflections on the table, the lamp, and the iPhone suggest that the user is sitting in front of a large window. The user is a woman wearing glasses and a tan leather jacket with shoulder pads. Her hands rest over the black keys as she contemplates your screenshot.
Drag & drop not supported, but you can still upload via this input field: