How to get a value of a field set with Media Custom Fields (programmatically)?
As taken from :
How does this plugin handle my data?
Media items are stored in WordPress just like regular posts. This enables us to use native WordPress functions to store and retrieve your custom fields. Due to this, your data is stored in a very future-proof way, in the postmeta table of the WordPress database.
So you would do it the same way you would do it for a post or page using
get_post_meta, but you would pass the media attachment ID in as the post ID