Is this a tick or a spider

I have been warned that there are ticks in my new area, but I've never actually seen them before. In the past when I Googled it, I thought they looked similar to spiders. I found this crawling on my dog's fur today and I just want to see if I can get a straight answer to know for the future. The linked picture was the closest shot I could get. Thanks!

http://i48.tinypic.com/1fk19v.jpg

Most definitely a tick

If it was clinging on to your dog's skin, it was a tick. Ticks suck the blood of mammals, but spiders want nothing to do with anything that is bigger than them.

You need to treat your dog immediately with a medication like Frontline. Ticks carry Lyme disease that can infect dogs. And humans too.