How to upload long images for screenshot or artwork in Steam profile showcases?

Open the browser console and enter the following lines of code for…

Upload as an Artwork:

$J('#image_width').val('1000');
$J('#image_height').val('1');

Upload as an Screenshot:

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