many-to-many relationship

Hi,

Say you have several objects (tables): person, location, event, etc. all
of which can have several images attached.

What is the best way to manage relations between a single 'image' table
and these different objects?

For now each 'image' row has pointers to id_person, id_location,
id_event, etc. (only one of which is used for any given row). 

Is there a better way, more elegant way to do it, without using
redundant id_* pointers on each row and yet still enforce foreign keys?

Thanks,

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