Working with multiple crop styles

I'm trying to figure out if/how manualcrop can be used in my use case:

• I have set up three image styles: Tall, Wide, Square - each with manual crop actions configured with aspect ratio of 100x200,200x100,100x100.
• In my content type, for the image field I have enabled Manual Crop and enabled the three image styles.

I want to/how can I:

1. Require users to select one (and only one) of the crop styles
2. When displaying the field, know which of the three styles was used

At the moment, I can see how you can require a specific style, but not how to require (any) one of the styles.
And when I specify a display style for the field, if the user has cropped with that style then everything displays correctly, but if they used a different style I can't see any way of knowing which style they used...

I'm probably missing something obvious somewhere :)