Maybe I'm misreading. It sounds like you're stepping the user up a pricing tier - e.g. going from 50 a month to 100 and then charging at the better rate.
I would also worry about a bug on my end that fires off lots of screenshots. I would expect a quota or limit to protect me from that.
I would also worry about a bug on my end that fires off lots of screenshots. I would expect a quota or limit to protect me from that.