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In the middle of a crazy chess game, a player checks his iPhone 6 for help from your app. The iPhone 6 lays next to the chess board in portrait view. The plays hand rests on a bishop preparing his next move. The iPhone 6 mockup will hold an image of 750×1334 px. There is not better place for a casual app.
Drag & drop not supported, but you can still upload via this input field: