Template:FileUrl/doc

By using Widget:FileUrl, this template allows local files to be used in CSS, anywhere which  is accepted. This is usually prevented due to the security risks of external images.

Note that the wiki doesn't count the file as being "used", and thus if there's no page which embeds the file with the normal  syntax, it will end up in Special:UnusedFiles and may get deleted. So make sure to properly use the file somewhere, like the documentation page for the template the file is being used in.

Example
Adding a background image to text: Heart can Heart can