how old is that photo? green leaves? haven't seen them for a month...
anyway: how warm is it and the relative humidity? I'd expect that if you leave the not-quite-warm car in very humid weather and then get back in (so drive, say, 3 miles to a store and get out, then get back in again 15 min later) while everything wasn't warm and humidity is nigh on 98%, temps below 5C.
Other than that, there's no reason for that apart from damp inside the car. You have checked it thoroughly (including the battery compartment), haven't you?
Bret