via a plugin like monkeybread, I believe you can edit EXIF data. there are no native functions though for editing metadata.
Metadata, as I understand it, is text data, so it belongs in a text field, not a container field.
EXIF data is embedded into images themselves:
The metadata contained by EXIF includes:
-Date & time
-Camera settings (camera model, ISO, shutter speed, aperature, etc..)
metadata by definition is just information about a file. It can be embedded as part of the file or separate.
Note that filemaker does have a GetContainerAttribute() function that can read some of the embedded file metadata out to text, but this does not change the method for how the metadata itself is stored.