This tool tries recreate a QR code from blurry QR code images by segmenting the image into n times n pieces and then guess whether the piece is white or black.
First, choose the dimensions (e.g. 29 for a 29x29 Version 3 QR Code, see wikipedia for QR code types). Then, upload the image. The tool will compute the result and also an annotated image of your QR code, with red dots where it thinks the center of each QR code block is (zoom in if you don't see the red pixels). If the red dots are off, use an image manipulation program to crop/transform your QR code.