Sorry, I can't pick up the link. You could post the picture here on MedHelp. They also have expert forums on this site, I am not sure there is one on dermatology but there might be. For a small fee, you could have a doctor look at the picture.
In any case, I again suggest a dermatologist. Some black marks might be nothing, some might be skin cancer, and there is probably everything in between in terms of seriousness or lack of seriousness. You need a real doctor who is sitting right there looking at your skin, to see it. Not even a photo online will do.
Ive got a picture here it is http://gyazo.com/c4c0b057fe0d8145791b1755f9d70ebb
See a dermatologist. Sorry, but it's hard to tell what that is.
It is about say half a center metre of less it doesnt cover up the whole tip
Talk to a dermatologist. At first I thought you were talking about a blackhead, and then I wondered if you were talking about frostbite (in other words, how big is the circle?) It might need a professional eye to tell you what it is.