I also stacked on the TwitPic's OAuth Echo Protocol a week ago.
The point was making header just like to request Twitter.
1. make OAuth Header to request Account/Verify_credentials to get JSON
not XML as result by GET method.
2. insert this header into X-Verify-Credentials-Authorization header
You make verification request header, and TwitPic send it to Twitter
as you send in TwitPic site. Remember the OAuth Echo was just an echo
The image file to send to TwitPic should be included as multipart/form-
I wrote a blog article for Ruby language and hope the code in the
article make some help.