how do incentive sites track actual signups?

do they have a tracking pixel placed on the conversion page for the offer or something? how do these scripts keep track of the actual leads?

if that's the case, how would you go about getting those pixels on non-incentive offers?

just thinking about something here...

Here is a blog post I wrote last summer about this very topic.

Most I have seen send the link through either their own system or something like adtrackz/prosper202 to append a subid to the end of the URL.

Each click will have its own subid which can be used to determine who clicked the link and completed the offer.