CHDK stands for Canon Hack Development Kit. This is a free (released under GPL) firmware add-on to the Canon PowerShot firmware that allows you to modify your camera in unimaginably vast ways. For starters, this includes overriding shutter open-time (from 64s to 1/100K s, with flash sync), R AW file capture, live histogram – the kind found in really expensive cameras – with RGB or ɣ overlay, customizable grids, user-written script support… and much much more.

In short, as the wiki homepage says, there are quite a few things that could not have been possible without CHDK: lightning photography, HDR (High Dynamic Range) photography and even unlimited DOF (Depth of Field) photography.

It does not damage or void the warranty of your camera in any way, since it is just a firmware add-on. There are quite a few tutorials on the wiki to put the CHDK on your Canon camera. In brief, here is a short tutorial.

1. Remove your SD card from your camera.
2. Connect the card to your computer (using a card reader) and format it – – make sure you backup your old photos before this step! A better way is to use Card Tricks, format the card as FAT and make it bootable.
3. Download the ZIP file for your camera from this page and extract the contents to root folder of your SD card.
4. Safely remove the SD card, and lock it for write-protection – this is an important step. The card must be write-protected, or CHDK will not run. This is a simple way to turn on, and turn off CHDK: remove write protection to use the default firmware, and lock it for writing to use CHDK.
5. Enjoy your new firmware, but make sure you read the user manual (check which version you want); CHDK is daunting and confusing at first.

For older models, such as Canon A430 (my camera, basically!), download the DISKBOOT.BIN file linked in this forum post. Both the pictures shown in this post were taken/modified with my Canon A430.