My Boston campaign's been going well, but I'm having some trouble adjudicating thaumaturgy complexity, specifically its use for "making the impossible possible."
For starters, are there any guidelines to follow for how much of a conenction there needs to be between the focus object of the ritual and the target? Say you're casting a tracking or locator spell, would a photograph be enough? I'm kind of thinking not, since all the cases I know of from the books and in the rules specify things like blood, hair, a True Name, or personal belongings. The more recent the target touched the item, and the deeper the emotional or metaphysical connection, the better the object is as a focus for the spell. I don't really think a simple photo would have a strong enough connection to attempt the spell, not unless it had some emotional significance like a picture of someone's wedding day.
Secondly, I know the rules say that the difficulty for such a spell should be based on how difficult it would be to track the target if it were possible to track them with the item used in the ritual. That's all well and good, but we don't get any guidelines on how to apply that reasoning. Should I be using a Stealth check for the target? This is really important because it's not just a case of deciding how difficult I want the attempt to be, but also of determining whether any extra time and work is needed to prepare the ritual.