How to recognize vehicle license / number plate (ANPR) from an image?

I have a web site that allows users to upload images of cars and I would like to put a privacy filter in place to detect registration plates on the vehicle and blur them.

The blurring is not a problem but is there a library or component (open source preferred) that will help with finding a licence within a photo?

Caveats;

1. I know nothing is perfect and image recognition of this type will provide false positive and negatives.
2. I appreciate that we could ask the user to select the area to blur and we will do this as well, but the question is specifically about finding that data programmatically; so answers such as 'get a person to check every image' is not helpful.
3. This software method is called 'Automatic Number Plate Recognition' in the UK but I cannot see any implementations of it as libraries.
4. Any language is great although .Net is preferred.

I coded a C# version based on JAVA ANPR, but I changed the awt library functions with OpenCV. You can check it at https://github.com/jivanro/ANPRMX_SourceCode