Why Does A Dog Lick Its Nose?

image credit: Andy on Flickr cc
When dogs are in their training stage a question that comes up a great deal is why do dogs lick their noses? While it's tempting to simply go with the old chestnut of an answer - because they can - there are a number of reasons why a dog might lick its own nose.
One thing is for certain sure, however: while they are doing it they often bring a smile to the faces of their human companions. As you can see from this spread of pictures, it's sometimes difficult to resist this particular canine photo opportunity.