After Canon stopped supporting the 350D (around 2007-2008), enthusiasts discovered that the firmware update mechanism had no digital signature verification on early 350D units. This allowed custom firmware to be flashed.
Official factory firmware manages the operational instructions stored directly on the internal ROM. Latest Official Version: Firmware 1.0.3 canon 350d firmware
Understanding the firmware of this camera is essential if you want to use modern memory cards or unlock features that were hidden at the factory. After Canon stopped supporting the 350D (around 2007-2008),
Overall, the Canon EOS 350D, with its original features and firmware updates, remains a capable camera for: Latest Official Version: Firmware 1
In 2005, Canon released a firmware update (version 1.1.2) that added the following features:
Flashing custom firmware on a 350D is for the casual user. Unlike CHDK on PowerShots (which loads from the SD card without permanent changes), custom firmware on the 350D overwrites the internal flash. If the flash fails or you upload a malformed image, the camera becomes an expensive paperweight unless you have a JTAG programmer and soldering skills.