Thank you all for your feedback. To have something to start with, I 
created a page within my TEI Wiki user page: 
<http://wiki.tei-c.org/index.php/User_talk:Martin_de_la_Iglesia/A_Guide_to_Images_in_TEI>. 
Feel free to discuss and add content (or merge/move/delete existing 
content) there. I think MediaWiki offers all necessary features, 
including the possibility to embed images and to render XML code. 
However, if you think the TEI Wiki isn't the most suitable collaboration 
platform for this project, please say so, either here or in the Wiki.

Best regards,

Martin

-- 
Martin de la Iglesia
Goettingen State and University Library
Metadata and Data Conversion
Papendiek 14
37073 Göttingen
Germany
phone: +49 551 39 14070
room: 1.411
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http://www.sub.uni-goettingen.de/