My verditius has a focus: Disguise. He has several effects that fall under this as he is a dwarf with an inferiority complex. I am considering an effect where one "strips" others of their diguises. It would be an MuIm(InMe) where one's thoughts are read and then one's image is modified to match their self-image, so that one actually appears to everyone as they see themselves. The intended effect is that of "stripping" any form of disguise (magical or mundane) from a person.
I think it would be funny if a spy kept checking his fake moustache but could not figure out why nobody seems to see it.
I think this would neatly fit into a focus: disguise, but what if the effect also stripped people of their metaphorical disguises, such as a way to counter guile rolls where the target is pretending to be someone else, even if their physical appearance has not been changed. Would this also fit the focus? Perhaps where it added some sort of symbolism to their appearance, like maybe, putting the appearance of blood on the hands of a murderer who is protesting his innocence. Hmmm, that might be straying into focus:deception. What do you think?
One problem might be with Demons.
Hermetic Magic is not able to pierce their deceptions.
If the spell fails to work , is the target by default a Demon?
(i would assume you boost the penetration for a device)
This is a Major Focus?
It seems broad enough for one.
I would peg the first effect, stripping a person of his mundane disguise, as an Intellego Corpus effect (either an InCo spell with MuIm requisites or the opposite, depending on which is easier - affecting the change or detecting the person's true appearance). This would suffice to override Im spells as well, I suppose, if the penetration is above the disguise's penetration or something like that.
A spell to counter other forms of deception, such as lying, I would not personally allow under the "disguise" focus - seems too broad a stroke, disguise is useful enough. At any rate, I would make this a Muto or Rego Mentem effect. Hermetic spells are more specific than "counter metaphysical deception", you need to be more specific with your spells. (IMO)
I would definitely not allow a spell to reveal the bloody hands of a murderer. Such "metaphysical deception" should be revealed by Second Sight, Vision, or other supernatural abilities - it is simply beyond Hermetic magic. (Although you could devise spells that mimic it to some degree.)
Yeah, I think that fits better. You could also use it to embarass people if you edited clothes out of the Muto'd image 
I think you are right. I think an InMe "find out what this person thinks is his greatest and most recent unconfessed sin", with a MuIM "change his image to include details of the memory". Perhaps this could create a floating 'ghost image' of a muder victim to orbit his head, but it would not actually detect and display sin, since that is outside the scope of hermetic magic. it would be pretty darn close though.
I think they would both be pretty cool frickin' spells though!
You can have some fun as a SG using this. Maybe someone murdered somebody, but does not think much about it since it is his position. However, he is cheating his best friend with his wife and you see the equivalent of a porno movie floating over his head. Your mage might even be quite interested in the image itself, if he is as weirdo as they are IMS. 
The answer when the murderer/cheater tells him why he is puting that interested face looking at thin air can get even more hilarious.
Cheers,
Xavi