All Images   All images in current directory will be used.

Selected Images   Uses currently selected images (marked with a blue frame).

To select several images in the Explorer at once, use the Ctrl and Shift buttons in combination with Left Mouseclicks.

Checked Images   Permanently selected images in current directory will be used (checkbox). This property is stored in the database.

Custom Images   Opens a dialog, where you can select images from folders.

Be careful with Include Subfolders, as this may lead to lengthy processing.