Instead of referring to an image included in an add-on, an image path may also contain the image directly as a Data URI (wikipedia). This can be useful for add-on icons in the PblWML (which may otherwise only contain core images) or for single-file scenarios.
Beyond these cases, Data URIs are less useful, as they are larger than the images themselves, and clutter up the files that include them.
A Data URI appears as follows:
It can be split into the following sections:
The `data:` part specifies that this is a Data URI.
The `image/png` part specifies that this is a PNG image. Also supported is `image/jpeg`.
Technically part of the mime type, this specifies that the image data is encoded using Base64.
The random-looking characters following the comma are the actual image data.
Creating a Data URI
Wesnoth does not yet support generating a Data URI for you, but there are alternatives.
There are a large number of Data URI generator websites. Googling for data uri generator will find them.
Creating a data URI by hand can be accomplished by taking your image, Base64-encoding it and formatting it as shown above.