When making pdf output, bg image becomes invisible

[nkjmsss]

If image is loaded like below (as bg image), bg image becomes invisible. It only happens in pdf output.

![bg contain](img/sample.png)

I'm using Mac OS 10.15.6 and Node v12.16.2.

[yhatt]

Didn't you see a warning message about local resources when generating PDF?

[  WARN ] Marp CLI has detected accessing to local file. That is blocked by security reason. Instead we recommend using assets uploaded to
          online. (Or you can use --allow-local-files option if you are understood of security risk)

Try using --allow-local-files option as written in warning.

[yhatt]

A reproducible example was provided in the issue tracker of Marp for VS Code (marp-team/marp-vscode#175), and I've confirmed not rendered background images in Marp CLI too.

Identify this issue as a bug, and going to find out a workaround to avoid a problem by upstream Chrome.

[yhatt]

We will patch for workaround in the next release: #294. If you are still using the current release, you also can try using --template bare option.