Using Canon Hack Development Kit (CHDK) you can super power your canon cameras. It supports a wide range of canon cameras (it includes the SX100IS showed above, and so many other powershot cameras).
Before proceeding two things need to be specified
1. It will not make any permanent changes, that means what ever changes CHDK will make is reversible.
2. No warranty – you will have to take the risks, it MAY harm your camera permanently.
What are the benefits you will get when you use CHDK ?
RAW file support – RAW files (also called as digital negatives) are files which are not processed.
Full manual control over exposure, shutter, aperture, focus and ISO
Motion detection – This facility allows you to trigger exposure when it detects a motion. This allows you to shoot even a lightning using a point and shoot camera.
USB remote
Bracketing
Live histogram
Zebra mode.
Run scripted actions
Before installation
You will have to find a version which is suitable for your camera, no version designed for a camera will work on another model. So make sure your camera is supported and you are using exact CHDK for it.
Check the list of supported cameras and download from this link
How to install
It is always better to do this on a SD card with out any other content, so first remove all the contents from it.
Copy the files downloaded and english.lng file if you want the language as English.
Switch on the Camera in View mode.
Use menu button and choose “Firmware Update”
It will install the CHDK and will restart your camera.
Canon Hack Development Kit is an open source project.
CHDK Wiki