You're right in that we can quietly take photos, descriptions, license plates, etc. and turn that over to the enforcement agencies. And yes, you don't want to be confrontational with them. No sense letting them know that we're documenting what they're doing. Ya gotta be "cool" about it. Seems like, when I run into people such as this, there is 2 of them, and 1 of me. Not good odds in my book!
To me, these guys are poaching, and as such, are stealing. They're stealing from you and me, and everyone else who loves the outdoors, and thus live to chase trout in a clear mountain stream or tailwater with only the noise of the wind and rushing water.
Posting on this Forum is a great idea, maybe we can all watch out for these people, and help the rangers build a iron clad case. They may not get any jail time, but hitting them in the wallet with a stiff fine will get their attention.