An HMM is just a model, not an algorithm. What is the task you want to accomplish? Feature detection, object tracking, mapping, compression, etc. ?
Your best bet when it comes to vision stuff is OpenCV. If this library does not have the algorithm or method you want, chances are that you will have a hard time finding a good implementation of it elsewhere. You might not find HMM mentioned too much anywhere there because, for many methods, it is, implicitly, the underlying model and thus it is not even worth mentioning.
Did you try Googling? There's plenty of code out there for this type of thing. One example, with a nice webpage to explain it. http://webdocs.cs.ualberta.ca/~lindek/hmm.htm That gives you the HMM part and you can get the camera code from OpenCV (I haven't looked under the hood of that library quite yet, but it seems like Mike is saying that a lot of their stuff is based on HMM anyway).