First element of multi-valued media field

Problem/Motivation

I have a custom content type with a multi-valued media/image field of which I only require the first value. As far as i can see none of the provided field enhancers is able to achieve this, so I will probably need to write my own.
I was wondering if somebody could get me started on this as it is not clear to me how to do it. I can see that I need to create a plugin extending ResourceFieldEnhancerBase, but that's about it. Any hint are greatly appreciated.