VK Web API (simple)

I would like to call the method "photos.get" and retrieve photos from a VK community.The problem is that I am unable to view the oid i.e owner_id( one of the parameters required for the request) when I visit the URL. For example, when I browse a certain community, I end up getting a URL like "http://vk.com/picsa".Instead of this picsa, I require a number that can be passed in as an argument. How do I get the owner_id instead from the URL?