Configuring image previews for different websites.
Some services such as Signal do not use the open graph protocol for previews; rather, they rely on linking an 'icon' attribute to the site.
Source: https://github.com/signalapp/Signal-Android/blob/ecfe218840d6fcea448219c3fb29051ac2311c87/app/src/main/java/org/thoughtcrime/securesms/linkpreview/LinkPreviewUtil.java#L33. This assumes that the icon to display for the website is linked as a favicon in the header of the precise page we are using. The Signal code manually parses the header of the website for the icon and displays it.