Since you are talking about CHDK, I'll assume you are using a Canon camera.

The software disc that shipped with your camera includes a program call EOS Utility that enables your camera and computer to communicate. Part of the functionality included in EOS Utility is the ability to shoot tethered. This allows you to adjust many settings in the camera using the PC including such things as Tv, Av, ISO, metering mode, drive mode, mirror lock up, etc. Hovering the mouse pointer over the shutter button has the same effect as a half-press on the camera's actual shutter button. Left clicking on the button on your screen has the same effect as a full press of the shutter button.

Depending on the selected settings, the image can be saved on the camera's memory card, downloaded and saved to the connected PC's hard drive, or both. You can also configure where the file is saved and automatically rename the file based on several factors ranging from the date and time to a user selected string or a combination of several of these factors.

Updates to EOS Utility are available from Canon's online service and support page at http://www.usa.canon.com/cusa/support/consumer In order to install the updates you need to have a previous version installed or the disc that came with your camera inserted in your optical drive.