The RPi educational materials include a short workshop on using the camera module. Part of this ("Camera programming: Capture when activated") demonstrates wiring and code to take a picture in response to an external button being pushed.
On the RFID side of things, it looks like the amusingly named RFIDIOt library is something that would enable Python to talk to several RFID readers.
So, assuming you have a RFID reader that you can connect to the Pi (and which is compatible with RFIDIOt), it shouldn't be terribly difficult to modify the recipe to your purposes: replace
GPIO.wait_for_edge with some code that waits for a valid RFID token, e.g.
card.select() and you should be well on your way. You'll probably find there's a bit of fine-tuning to do (you may have to implement some form of debounce - I'm not familiar enough with RFID to know if this is an issue), and of course the script needs modifying to continually wait and take pictures instead of stopping after the first one.