import - How to extract a specific element from EXIF photographic metadata?

It's now possible to import photographs into Mathematica and import the EXIF data at the same time:

i = Import["ExampleData/coneflower.jpg", "ImageWithExif"]

You can now look at all the metadata:

Options[i, MetaInformation]

{MetaInformation -> {"Exif" -> {"ImageDescription" -> " ", "Make" -> "NIKON", "Model" -> "E950", "Orientation" -> 1, "XResolution" -> 300, "YResolution" -> 300, "ResolutionUnit" -> 2, "Software" -> "Adobe Photoshop CS3 Macintosh", "DateTime" -> "2008:08:19 11:29:05", etc...

So how would I extract - say - the exposure time ("ExposureTime")? I was trying something like this:

"ExposureTime" /. Options[i, MetaInformation] ...

but I don't know enough about the structure of the stored metainformation. Can you do this without knowing that structure?

Answer

Does this do want you want?

Cases[Options[i, MetaInformation], 
 HoldPattern["ExposureTime" -> ___], Infinity]

or even simpler because it is Rules all the way down:

Cases[Options[i], HoldPattern["ExposureTime" -> ___], Infinity]

{"ExposureTime" -> 1/65}

All-in-one:

With[{wanted = "ExposureTime"}, 
  wanted /. Cases[Options[i], HoldPattern[wanted -> ___], Infinity]] //
  N