Seeing how far a slave will go/ideas for punishment...

I'm training a slut Nick, but this is my first time being a master. He begs me to force him to do humiliating things and be my slave, but I run out of ideas somewhat fast.

He said he's willing to do ANYTHING. What should I do to test him? He said he would show me photos of everything I tell him to do. I'd post them here of course. He said he'd do the dirtiest things. Any tips of ways to humiliate him more? Any thing you'd like to see in his ass?

In general, what are some good ideas for punishments? So far I mostly just force him to use a toy in his ass and swallow his cum. But I need more ideas.

We're kinda far apart now so we mostly just talk online. But he has a digital camera and webcam and phone. He wants to be a dirty whore for me.

Thanks! :)