Currently we use this extension:
[url removed, login to view]
In our live store we have more or less 100 products with 20 images each (always the same). We have developed a new image set (20 new images) and now we need to substitute the old one with this new one.
The extension doesn't provide an automatic system to substitute all these images automatically, so I think that have to be managed using mysql and working directly on the database.
Contact me for more technical details about it.