There's only one origin point, but I think you mean image points.
Oops yeah I meant image points.
I'm pretty sure there's no hard limit to it, I also don't think there's much of an issue with having 20. Maybe there will eventually be some performance impact since the position of these image points have to be tracked through all possible image manipulations (translation, rotation, mesh deform,...) which I'd assume adds some math overhead. But that overhead is probably very small so I'd not worry too much about it.
Okay makes sense. Thanks WackyToaster!