Clear New Tab can't automatically download a theme image if a theme is paid, but you still can upload it manually. Go to the Clear New Tab options page and click on the "Link to theme image". In the opened tab, right click on the theme's image and select "Copy image" from the context menu. Return to the Clear New Tab options page and paste the copied image in the "Paste image or URL" text field. Then, select the "Left top" option from the "Background position" drop-down, "Repeat X" from the "Background repeat" drop-down and set the #212121 color in the "Color of area around background" color picker.