Image attribution and metadata

[doofus-01]

Wesnoth is what it is because of the efforts of many people. Code contribution has been tracked directly with svn or git, but credit and copyrights for artistic contributions has been a more manual process. In an effort to streamline the attribution and copyrights, we now require the following information:

1. Author - This will be saved as EXIF "Artist" tag in *.webp, *.jpg and XMP (dc) "Creator" tag in *.png
2. Copyright - This will be saved as EXIF "Copyright" tag in *.webp, *.jpg and XMP (dc) "Rights" tag in *.png
3. Creation date - This will be saved as EXIF "Create Date" tag in *.webp, *.jpg and XMP (dc) "Date" tag in *.png
4. Comments (any other information you need to include) - This will be saved as EXIF "User Comment" tag in *.webp, *.jpg and XMP (dc) "Description" tag in *.png

As a contributor, you do not need to worry about EXIF/XMP metadata details, but you do need to provide the information above.

The reason for the XMP metadata in *.png is because this is what can be read and written with GIMP and Photoshop. For GIMP, navigate to Image->Metadata->Edit Metadata and edit the "Description: Author" and "Description: Copyright Notice" to include the critical data.

A simple CLI tool to edit metadata outside of the image editor is exiftool (https://www.exiftool.org/index.html). An example of what would give the needed info (while not leaking unintended data) is:
exiftool -all="" -overwrite_original -XMP:Creator="<your name>" -XMP:Rights="CC BY-SA 4.0" -XMP:Date=now -XMP:Description="<whatever text>" <filename.png>