I have few things.
Your captcha is a pain might look for a easier to read one.
Your script does not give a notice if submission was successful or if it wasnt.
Now to proxylist 101 you are requiring proxy owners to give you a link when your site is new and not sending enough traffic to deserve a link back. Some proxy sites have good rankings and PR that would benefit you lack of traffic that wouldnt get anything in return. In fact it would work reverse you would get traffic from people clicking the links in the footers of the proxies,
Solution Est. your site then require backlinks. Invite proxy owners to submit without a link and you will get a fair amount then you can start in on the promotion. Remember proxy webmaster forums would not be the right place. Stick with sites that would have users looking for or needing proxies.
Once your site grows up then you can change over your policy to require back links.