Help - QR offline Decoder
Features:

- Does NOT need an internet connection (does not upload your images to a web service)
- You can either shoot a picture with the cam or pick one from your media list
- Supports detecting from "live" feed
- Supports QR-Codes and some other barcodes

Usage hints:

- A focused pictured is important:
  It is not really important how large the code picture on your image is. Choose the distance so that the code just fills the circle in the middle of the finder. (The Pre3 should have an autofocus camera, so this may not be important on such device)
- When taking pictures from displays it often helps to make the picture on the screen larger (zoom in)
- The live mode just takes pictures until detects a valid code - the faster your device, the more pictures it analyzes per time.

Also you might want to have a look at the Wiki.