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[Deus]

as stated, take the dimensions of an image and create keywords from them.
Example: 1920 x 1200 would be 1920 and 1200
has anyone created this plugin at some point?

[Αndré]

As far as I know such a plugin doesn't exist yet. As the needed data should be already available in the SQL database, a simple query will solve it for already existing pictures. If you need it for future pictures, too, you either have to run the SQL query as a cronjob (not recommended), create a plugin (should be quite easy by using the add_file_data hook) or a mod (just append it to $keywords in include/picmgmt.inc.php).