Library Features:
+ rename erase* methods that access a file to remove* 
+ add ExifData::erase(tag)
+ Thumbnail support: set (re-calculate)
+ operator>> for Value, since we already have read()?
+ Use size_t where appropriate
+ Support TIFF type ids
+ Support for broken IFD makernotes (which have corrupted IFD offsets)
+ Support non-intrusive deletion of entries from an IFD.
+ Write an example using low level IFD classes to print summary Exif info
+ Extended JPEG support (actual resolution of the image)
+ Implement proper error handling
+ Complete support to create Exif data from scratch:
  + set thumbnail, write thumbnail tags
+ Make it possible to force write from metadata (just an optional arg to write?)

+ Make Image::doWriteMetadata do its work in a single pass

+ Revise Image and IptcData+ExifData API (aka turn it inside out)
+ Add PSD images support (and TIFF, NEF, CRW...)
+ Add support for XML metadata files

Exiv2 functionality
+ Add offset to value for hexdump (requires metadata to have an offset)

Bugs:
+ Handle all Todo's
+ Cleanup and fix implementation of JpegImage (must be able to read any APP0/1),
  should be able to insert exv into extracted thumbs (usually w/o APP0/1)
+ Review Image interface. Is it really necessary to have so many functions there?
+ Review the handling of type ids? What if we encounter type 27 in an IFD?
+ Rational and other output operators (see Josuttis, p653)
+ Through ExifData::iterator and Metadatum::operator= it is possible to have 
  multiple copies of one metadatum in the metadata container
+ Checks and non-intrusive updates must be atomic, i.e., not change anything
  if the metadata is not compatible
+ Review: Exception safety
+ Review: Ifd1 only at Thumbnail, do we really need Thumbnail::update() ?
+ Should JpegImage differ between NO Jpeg comment and an empty Jpeg comment??