It seems the problem is with file permissions (say, bit 'x' set for graphics files). I will re-install the Serendipity and report whether there are errors.

Indeed, when the permissions have been reset, the problem was gone.

Sorry for the false alarm.

I have decided it would be the best to register here.

The details I didn't mention: PHP is run in CGI mode, mod_rewrite mode is used (it is clear, of course, from the contents of .htaccess). iconv isn't available, the rest of Serendipity recommendations are met.

PHP version is 4.3.11.

I can send ...