The area to the side of your dog's nose looks like he has a sinus infection and it is draining and crusting. I often foster dogs from lcoal shelters and, when they have sinus infections or an upper respiratory infection, I usually see this green/yellow crusting on the edge of the nostrils. He might need to see the vet sooner than later if he is having any symptoms of an upper respiratory tract of sinus infection.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge