libcamera-jpeg -o pic.jpg 
libcamera-jpeg  -n --width 4608 --height 2592 -t 2000 -o pic.jpg 

# max resolution (for this picam3), with mjpeg coding (size not working in h264)
# this will give *low* frame-rate .. camera limit is ~14fps, and slow pi-zero can slow to more like 1fps
libcamera-vid --mode 4608:2592:16:U --width 4608 --height 2592 -t 6000 --codec mjpeg -o outfile   

# alternative, giving jpeg output (separate, sequentially numbered) 
libcamera-vid --mode 4608:2592:16:U --width 4608 --height 2592 -t 6000 --codec mjpeg --segment 1 -o test%05d.jpeg