So, you want to take a bunch of photos, but don't want to burn the SD card on the raspberry pi?  Place the files on a ramdisk.

Make the ramdisk

sudo mkdir /mnt/ramdisk

Edit the rc.local file

sudo nano /etc/rc.local

Add the lines above exit 0

mount -o size=30M -t tmpfs none /mnt/ramdisk

/bin/chown pi:root /mnt/ramdisk

/bin/chmod 777 /mnt/ramdisk

Reboot, then check the file structure with

df -h

Now, when you use raspistill, direct the output to the ramdisk

i.e.,

raspistill -n -t 2 -o /mnt/ramdisk/test.jpg

Let's say you want to use the raspberry pi to take a bunch of fast timelapse pictures (i.e., 1 second between pictures).

First, you kick off the raspistill (this command will work with SSH too!)

nohup raspistill -n -t 0 -o /mnt/ramdisk/test.jpg > /dev/null 2>&1 &

Then, find out the PID with:

pgrep raspistill

Then, whenever you want a new picture to be taken, you use the "kill" command to send the message to raspistill to take a picture:

kill -USR1 12125

where 12125 is the PID you found using pgrep

Then, you can rename the pictures or network copy them.  I think raspistill also takes in an incrementing filename.

Don't forget to kill the raspistill process when you are done!  For example,

kill 12125