You can export any page in a prototype in Atomic to a PNG image.
To export an image of a page, select the page in the Pages panel on the left side (or make sure you have un-selected any elements on the page you have been working on).
In the Properties panel on the right, below the page properties, you'll see an option to 'Export Page as PNG'.
Click the 'Export Page as PNG' button, and the image will automatically download.
Handing off to a developer
If you need to hand off the prototype to a developer as part of your workflow we recommend inviting them in as a collaborator to the Project.
This will allow them to see all of the element properties of your prototype. Just add them using the Plus button at the top of a project or read more on Collaborative Design in Atomic.