Carpenter is a fascinating case and you're astute to bring it up. If the tracking image were capable of actually tracking the entirety of someone's location (the way CSLI is), then Carpenter would probably apply.
Assuming it is just a normal tracking image, though, it doesn't provide "detailed, encyclopedic, and effortlessly compiled" information about someone's activities - just whether they opened that particular email while displaying remote images, and - if so - their HTTP request. I think it's unlikely this fits the facts under Carpenter.
Also, Carpenter was about a warrantless search. We really have no idea if the prosecutors did this on their own initiative to try to address the violation of the protective order, or if they did it at NCIS's behest after a warrant. It's entirely possible that this is at NCIS's initiative. Still a lot of facts to uncover here.
Assuming it is just a normal tracking image, though, it doesn't provide "detailed, encyclopedic, and effortlessly compiled" information about someone's activities - just whether they opened that particular email while displaying remote images, and - if so - their HTTP request. I think it's unlikely this fits the facts under Carpenter.
Also, Carpenter was about a warrantless search. We really have no idea if the prosecutors did this on their own initiative to try to address the violation of the protective order, or if they did it at NCIS's behest after a warrant. It's entirely possible that this is at NCIS's initiative. Still a lot of facts to uncover here.