Despite many people's beliefs, yes. Smalltalk can be restarted from scratch. First, the images are paired with a serialization of the source code. If you used nothing else you could restore the source in an image via that, it can also be used to produce diffs for distribution. That's not the best way, but it is a viable way.
The better way is tools like Iceberg and its various predecessors (Iceberg is nice because it works with git which has become the industry standard at this point for version control). There, you select down to the individual method what you want to commit and you can push it to other git repos on services like Github.