eyes_cascade.detectMultiScale( faceROI, eyes, 1.1, 2, 0|CASCADE_SCALE_IMAGE, Size(30, 30) );

This line of code is using the "detectMultiScale" method of the "eyes_cascade" object to detect eyes in the "faceROI" region of interest. The parameters used are:

- "1.1" - Scale factor used to detect eyes at different scales.
- "2" - Minimum number of neighbors required for a region to be considered a potential eye.
- "0|CASCADE_SCALE_IMAGE" - Flags used to control the detection process. In this case, "0" means that no special flags are used, and "CASCADE_SCALE_IMAGE" means that the image is scaled to different sizes during the detection process.
- "Size(30, 30)" - Minimum size of the detected eyes.

The "detectMultiScale" method returns a list of rectangles that represent the detected eyes in the image.