Loop are used to repeat a block of code or subscript until countdown are completed.
Set loop command:
loop *id *seconds call *subscript
Close Loop command:
close_loop *id
Script example:
make_sub myimg
sub myimg photo_now 640x480 myphoto
# repeat the loop process(myimg) ,and restart each 30 seconds.
loop myloop 30 call myimg
# wait 10 min.
sleep 600
close_loop