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This casual setting with a black Nexus 7 will do wonders for your mockup. The Nexus is laying on a wooden table with a dark finish. In the background there is an out of focus orange chair. You can insert a 1920x1200px image in landscape view in the Nexus 7. Your mockup will look great in this warmly lit set.
Drag & drop not supported, but you can still upload via this input field: