Image attachment Exif should be stored in individual post meta entries

[markjaquith]

Currently, image Exif information is stored in one big serialized post meta entry. This makes it impossible to query against an individual entry (for instance, querying all images shot at 50mm).

It's easy enough to separate them out with an upgrade routine, and have new images put each Exif value in its own post meta entry. The question is backwards compatibility. Should we drop the old serialized info? Should we leave it and just not ever update it? We could make a compatibility layer (would involve a filter on postmeta updates that looks for changes to the individual keys or the serialized key, and sync changes made in one to the other).

My vote is to leave the old data, but not populate it for new attachments. Thoughts?

Punting due to time constraints, will reconsider for upcoming release cycle. Media changes planned for 2.9/3.0.

#6819