Apple made taking a screenshot (screen capture) of your iPad screen super easy: Press the home button and power button at the same time. Your screen will flash white and you'll hear a camera shutter sound effect. An image of your screen as it appeared will be saved to your Photos.app Camera Roll.
As of v2.3.1, Photosmith uses the Camera Roll as a storage place for its photos. Thus, iPad screenshots will appear in Photosmith. However, because iPad screenshots are saved as a PNG file, it cannot be synced to Lightroom because Lightroom doesn't support PNG.
As we continue to refine the Photosmith app and associated Lightroom plugin, we will bring parity to file formats supported by Photosmith.