Image Conversion

Hi -

Any advice how to convert all images in an epub?
There is more to it than un-zipping, bulk converting and re-zipping as the format may change from jpg to gif (which can save a lot of space for non-photographic material) and references would have to be updated.

The purpose:

- Save bandwith, especially when mobile
- Make books snappier to load
- Fit books into Google Books which has an upload limit of 50MB

Thanks!