Requires iOS 5 or higher
Camstamp adds the ability to embed a digital-camera-like timestamp in any photo taken with the default camera app.
Camstamp allows customizing the color and font of the timestamp. There is also the option to duplicate the image and timestamp just the copy, in order to keep an original copy.
As a precaution this option is enabled by default and can be disabled in Preferences.
Be sure to check out Dater if you only want timestamps to be displayed in the photos app.
Configure options from Settings app
See larger Screenshots below..