Looking at the rest of the underside of the vehicle--is the light area in the upper left corner a dry spot with the rest darkened or shiny due to oil or other fluid? Or is this the result of camera/lighting induced artifact?
Really tough to tell when parked on a surface like loose rock. Tough to tell from that photo, as I can't see anything dripping. But this time of year, water coming from the A/C drain is a strong probability.