Your Twitpic page is easy to find (to be honest I think everyone has one by virtue of being on Twitter, something that initially puzzled everyone but we soon came round), it's
http://twitpic.com/photos/yourtwittername so mine is http://twitpic.com/photos/JoBrodie
How to download your picsYou can download your pics by clicking this link: Get your Twitpic pics, then logging in by authorising via Twitter, then scrolling down the resulting page (past Mobile, Privacy, Linked Accounts and Delete Account) to Export your photos, then click on the green button saying request your data - it looks like this.
Once clicked it will start processing and you'll see this - I don't know yet how long this will take (presume it depends on the number of your photos).
If you want to be helpful / annoying, search for Twitpic on Twitter and filter it by people you know (you can only do this on Twitter dot com) and then tell them to do this.
Twitpic is shutting down post updated in October (4 September 2014) Twitpic blog (same as linked above).