[Image-SIG] conflict between various library to process EXIF data

[Bram Mertens]

Hi,

How to read and write EXIF data from images has been discussed several 
times before but I could not find a discussion on the problem I've run 
into when using multiple of these.

In short: after adding a comment to the EXIF header using the 
setComment(...) and writeMetadata(...) methods of pyeviv2 
(http://tilloy.net/dev/pyexiv2/doc/release-0.1.2/pyexiv2.htm) the EXIF 
header is altered in such a way that it is no longer possible to read 
the EXIF header with EXIF.py.
Furthermore  imghdr does not even recognize it as a JPEG anymore.

 >>> import imghdr
 >>> type = imghdr.what('DSC02299.JPG')
 >>> print type
jpeg
 >>> type = imghdr.what('20070623-171634-DSC-H5.jpg')
 >>> print type
None

Also the file command in Linux no longer recognizes the EXIF header:
before:
$ file DSC02299.JPG
DSC02299.JPG: JPEG image data, EXIF standard 2.21
after:
$ file 20070623-171634-DSC-H5.jpg
20070623-171634-DSC-H5.jpg: JPEG image data
(Note: part of the processing done is to rename the image based on the 
date in the EXIF header)

I switched from EXIF.py to pyexiv2 because the first does not provide a 
method to add a comment to the header.  Considering the fact that 
EXIF.py appears to be no longer under active development I simply 
replaced all my calls to EXIF.py with calls to the relevant pyexeiv2 
methods.  However imghdr is part of the standard library so the fact it 
will not recognize the image anymore makes me wonder if maybe pyexiv2 is 
doing something "wrong" that might cause other problems later on.

Can anybody provide insight into this?

Thanks in advance

Bram