NOTE; This should go into a console, on the steam website. You should know what to do.

Artwork Showcase:
$J('#image_width').val(1000).attr('id',''),$J('#image_height').val(1).attr('id','');

Workshop Showcase:
$J('[name=consumer_app_id]').val(480);$J('[name=file_type]').val(0);$J('[name=visibility]').val(0);

Screenshot Showcase:
$J('#image_width').val('1000');
$J('#image_height').val('1');
$J('[name="file_type"]').val("5");