Icon when linking from Facebook

When I link to a post that has no images on Facebook, the icon that Facebook uses is not the favicon, but an image with three greyish blue vertical bars of different sizes. Does that come from the theme and if so, can I change that?
Of course I can manually edit the image, but I often forget that since the image is only shown after posting on Facebook, it is not part of the preview.

• This topic was modified 6 years ago by Roy.