Taking Photos and Video

What is the name of your state? Maryland

How can I find out whether it is legal for me or a neighbor to photograph or videotape someone performing illegal activities when the subjects are on THEIR own property and I am on my property or public property (ie., the street)? Purpose of obtaining photos/video is as evidence to bring charges against the subject.

Are we venturing into territory where we could get in trouble, and should really be hiring a private investigator or something like that?

Depends. Are the activities you are taping visible to you without enhancement? For example, do you have to climb a wall and push bushes out of the way in order to view the activities?