You are within your rights to film trespassers on your property. You can also advise the police this is what you intend doing and why before you start any filming if you have any concerns about 'inappropriate filming'.
You need to take action of some kind if you want to protect your rights. As pointed out earlier you need to find out what rights are involved with the easement, then you should take steps to exclude anyone not given rights by the easement. That is your starting point.
That is a good idea advising the police of your filming... They will also point out any ways it could be legally problematic