PlaceIt, by Breezi, is a free service that allows you to upload web or app prototypes image and generate screenshots of your apps in realistic environments.
The service has multiple environment themes, to get started, first you need to select the environment from the horizontal selection tool. Then just upload or drag&drop the JPG, PNG image of your app (or pull from the web via a URL), over the active environment and Placelt will automatically render the screenshot in a realistic environment theme.
It also allows you to share the generated image on social networks ( Facebook, Twitter, Google+, Pinterest), save it to your computer, or you can just copy the unique Breezi link which you can use to share with others.
PlaceIt-generated-images are free to use for commercial purposes if you refer back to PlaceIt when the generated sceenshot are commercially used.
As of now, PlaceIt supports uploads for screenshots of Kindle Fire, Nokia Lumia, MacBook Air/Pro, iMac, Google Nexus, Galaxy SII/SIII, and Microsoft Slate. New themes are being added and they’re also allowing others to contribute photos for use in the web. Breezi team will credit the photo to you (if your photo gets selected) with a link back to your site
Overall, this service works great and proves handy when you quickly want to generate screenshots of Web apps to present to other people (clients, friends ) in a real world like environment.