Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Once you are SSH'd in navigate to:

/Applications/Cydia.app/sources

But it appears that they are stored as .png ..... so I'm not sure if that helps.
 
Cydia uses APT. You'd add sources in the same way you would using Debian, Linux for Children (Ubuntu), etc.

It also doesn't store them as images. Those are images.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.