Just over a year ago I mentioned a nice library for creating PSD formatted files called PSDWriter.
Here’s a handy library that utilizes PSDWriter from Vinh Phuc Dinh called MMLayerShots.
MMLayerShots allows you to take app screenshots and automatically convert them into layered PSD files so you can then load them into an app that supports PSD files (ie. Photoshop, Pixelmator, Gimp).
This allows you to adjust the individual elements without having to cut apart each element individually.
You can find MMLayershots on Github here.
A handy library for experimenting with app designs.