fudgey: can you please elaborate? i wish for a person to take a photo, be displayed for a few seconds, and be deleted immediately.
by 'be displayed' i mean the image that shows up immediately after a photo is taken, not in 'play' mode.
Actually CHDK can change between REC and PLAY with script commands at will. But if what you said above is all you need, you don't need to switch modes because you can Canon's built-in "erase durings shutter hold review" feature (if your camera has that -- consult the manual).
In case this feature is not known to you, this is how it works: Fully press shutter to take a photo. Don't release the shutter. The camera takes a photo, writes it to the SD card and shows the photo on the screen for as long as you keep the shutter pressed down.
While still fully pressing the shutter, press the erase (trashcan) button. The camera will ask for delete confirmation. Press whatever keys it takes to select 'yes' and the file will be gone and you'll be back in live view REC mode.
You can write a script to emulate these keypresses, it will be roughly something like this (in pseudocode, from my vague memories of this feature without testing on a camera):
press shoot_half
wait for focus etc if you wish, in a shoot state loop if you wish, set overrides if you wish
press shoot_full
sleep seconds*1000
press erase
sleep 100
release shoot_full
sleep 20
release shoot_half
sleep 100
press left
press set
