I've mentioned Placeit before. It lets you upload screenshots and frame them in high quality stock photos of any device. Since the last time I've mentioned it, they've added the ability to put screen recordings into devices and save as video, as well as a whole section of t-shirt and poster mockups with models and settings. (It appears to be what [Teespring](https://teespring.com/stores/lab) is using now for the marketing photos they generate for user campaigns.) It's not cheap ($8 for a one-off high-res mockup), but the quality is worth it for anyone serious about marketing.
