File used by Chameleon Clock, a program used to customize Windows wallpapers; contains a background image, preview images, and several other images containing graphics for displaying the current time; used to synchronize wallpaper graphics with the system clock time; stored using Zip compression.

WCZ files contain .JPG and .PNG files. The background and preview images must be saved as JPG files. The time-of-day image files must be saved in the PNG format and use the naming convention monthX.png, dayX.png, hourX.png, and minuteX.png, where X is the 0-12 months, 1-31 days, 0-23 hours, and 0-59 minutes. WCZ files may also include moonphase, AM/PM, and zodiac graphics. Chameleon Clock wallpapers may range from 800x600 pixels to 2560x1600 pixels in size.