Hans,

> no time for a detailed answer now, but in xml mode you can make { } 
> letters which solves the problem

Could you please elaborate a bit?  I'm not familiar with ConTeXt's XML mode (other than for processing MathML).  One thing that I suspect is that XML mode would have an issue with '<' and '>' in the filenames.

Another thought: The image filenames are encoded in my original xml documents according to RFC 1738 (http://www.blooberry.com/indexdot/html/topics/urlencoding.htm).  In my XML -> ConTeXt XSL stylesheets I'm decoding those filenames.  Would it be useful for others if the externalfigure could understand url encoded filenames similar to something like this:

%
% includes the file "flower{1.jpg"
%
\externalfigure[flower%7B1.jpg][encoding=rfc1738]

This would give ConTeXt a general-purpose filename escaping mechanism.

Cheers,
Mike