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I don't know how to describe exactly what I'm looking for, but I've seen a service which allows me to take a mockup or illustration and put it realistically in pre-made images of a Mac and iPhone.
But I can't recall where I saw it or how to do it. I don't want to take, for example, a flat image and then figure out how to fit it and rotate it into a stock Mac laptop image.
I am pretty sure I saw an app which did this, but I can't remember it, or perhaps there's an easier way to do this.