I'd like to take a picture in the exact spot as another photo I've take a while back.
To help lining up the shot, I wonder if it would be possible to overlay the camera app with a semi-transparent version of the older photo?
In order to do this you'll need to create your own CameraPreview and modify the
SurfaceView so that there is an image overlaying it.
You can find the code that you need to control the camera and create a camera preview here:
Once you have that, you'll just need to manage the overlay and make sure the dimensions line up, etc.