I administer a couple of servers that offer a final world download. The world is a collectively produced work of art.

Interested parties are able to start up a server with a downloaded world, or run it single player, but would typically not have the technical know-how to set up a full Bukkit/Spigot/PaperSpigot server with the ImageOnMap plugin. And, in the absence of the plugin, the result would be disappointing: blank maps wherever custom map art was used.

Looking at the map data files in world/data/map_N.dat, e.g. for maps copied with Ctrl-MiddleMouse, I see that those files are only 197 bytes, whereas full written maps are 1429 bytes.

I wonder whether it is possible to fully save pixel data so that they are viewable in the absence of the plugin, possibly by setting the map locked and/or the associated world null through the API?

That can be a nice feature but we don't know for sure if it is possible, for the 4.1 we are planning to change where maps are stored #36.