A tease for two...
This part can be tricky.
If you want to ride him, or let him fuck you, you can. You're in control after all. You do risk him cumming.
Tell him that if he cums, you will email that picture out right away. Perhaps you could load the picture on your computer, and briefly take off the blindfold to let him see it. You could even open up your email account and scare him further.
Now keep in mind if you do actually send it, you will have played your card, and potentially really mess up his social circle. It's a great power that you now wield over him. The point is to make him understand that. If he complains, tell him that he brought you into this, and that this is what he wanted.
That should be a pretty powerful incentive for him not to cum without permission.
Keep his hands tied though, because he may try to take over and start deleting the pictures. :)
If you don't want him to enter your pussy, continue on. If you do then just take great care not to push him over the edge. You can alternate making him use his mouth and dick on you until you orgasm.
When your ready, press continue.