Wallpaper:
First, create a directory named "wallpaper" in the root directory of USB disk,
and then put wallpapers in the directory. Max capacity of the directory is 20 pictures.
The size of each wallpaper is smaller or equal 30K. There is no limit on the name and
format of the wallpaper. It supports format of jpg, png, bmp etc.
Note:
If the size of each user photo and attendance photo is smaller or equal 10K, the device can
store 10000 user photos and attendance photos in total.
