Is it possible to lock the dynamically created stamp using javascript

Are you sure this is a good idea? What if you want to move, resize or delete the stamp after applying it? Locking it will make it impossible to the regular user.

Yes, there are a couple of ways to do this. Which one you use depends on what you are trying to achieve.

1) annotations have a "lock" property that when true keeps the user from being able to move the annotation. But otherwise the annotation keeps all of it's properties and the lock can be removed.

2) Annotations can be flattened, which makes the graphic on the annotation part of the page content, and all of the annotation features and properties are completely removed. All you get is the image on the annotation. And the original annot cannot be recovered.

Neither of these operations can be part of the stamp script. The script that either locks or flattens the annotation must be run from a different context.