You can store your downloads in your account when you signup!
Get a perfect side by side comparison of your app or website mockup on an iPhone and iPad. They are set on a light grey work station above a wireless keyboard.The iPad is set to landscape view and holds an image of up to 1024x768px. The iPhone is set to portrait view and would be perfect for a 640x1136px. This would work perfectly with an app that you can set your keyboard up with.
Drag & drop not supported, but you can still upload via this input field: