anpr

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; I know nothing is perfect and image recognition of this type will provide false positive and negatives. 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;