Phil, thank you again for the quick reply. Yes, I'd started to look at the sample config file but being new to Perl the syntax got the better of me. Not your job to teach me Perl, I know! What's confusing me is the kind of hierarchy that we seem to adding to. I'd like to define, say, Mytag1, Mytag2 and Mytag3 within an XMP namespace called, say, myNs. How would the sample look? This is how far I've got. I'm not really clear on what the GROUPS element is for %Image::ExifTool::UserDefined::myNs = ( GROUPS => { 0 => 'XMP', 1 => 'XMP-myNs', 2 => 'Image' }, #not sure what the third leve 'image' is doing here NAMESPACE => { 'myNs' => 'http://ns.myNs.com/xxx/1.0/' }, WRITABLE => 'string', # now I get stuck: Since I'm defining a tag (not its value) what else do I have to put in the curly braces. Your sample seems to add a further assoc array within the tag elements ?? Mytag1=> { }, Mytag1=> { }, Mytag1=> { }, ); Sorry to harrass but this is clearly the best tool for the job and I'm super keen to get this demoable. Thanks again. Mark