i recently tried to create a thumbnail of a jpg file which was not completely uploaded (corrupted file). it brought plogger to a screeching halt with a bunch of ugly debug code. i thought it would be helpful to at least highlight the main error, and also clue the person in to what the offending file was....
for example, i edited phpthumb.class.php, line 2059: $this->ErrorImage('<p><br><h2>All attempts to create GD image source failed ('.($GDreadSupport ? 'source image probably corrupt' : 'GD does not have read support for "'.$imageHeader.'"').'), cannot generate thumbnail. (File:'.$this->sourceFilename.')</h2>');
basically, all i did was highlight the final error with h2 tags and include $this->sourceFilename