1. a global git commit is done in the TiddlyWiki directory;

2. a diff tiddler is calculated (and a git commit --amend is done, to include it in the commit);

3. all tiddlers and image files are rsynced to another local directory (say, pao-copy).

4. in pao-copy, all image files are externalised, and the public tiddlers are rendered;

5. finally, pao-copy is rsynced to the live server (the raspberry pi).

All in all, this is a quick procedure. There are possible optimisations in steps 4, by only externalising the new images.