INFLD supports the keyboard command (Control-P) to capture a picture (or "snapshot") of the screen; see Screen Pictures. To use this capability under program control, use MX_SCRNPIC.
Having INFLD Generate Automatic Snapshots
If you specify the type code |S (vertical bar, capital S) in an INFLD call, it will automatically generate a screenshot (appending it to the current BUF file) on exit from the field. By adding SBR=INFDEF:|S to miame.ini, you can arrange to create a "slide show" of an entire session. This can be helpful for creating documentation, or for monitoring background processes, or for "snooping" on users (or simply for filling up the disk and creating useless system overhead.)