If the situation is bad enough that you can't get to a console session from the login window, you can do this in Single User Mode.
Hold down command-S when you hear the startup chime.
You can release these keys when the screen turns black with white text scrolling by.
Eventually, the text will stop scrolling and you will be looking at a command prompt.
The first commands you are going to type before doing anything else are:
fsck -y This will run a filesystem check on the boot volume, and fix any errors. Always a good idea when starting up a single-user-mode session
mount -uw / This will unmount the root filesystem (your startup volume), and remount it with read/write ability. You are making changes, so you need the write ability.
Next, cd into you Desktop folder.
cd /Users/<short user name>/Desktop replace <short user name> with your short user name; the abbreviated name that you use to log in or confirm admin access when present with a security dialog. If you don't know your short user name, just cd /Users/ and then type ls. You should see your short name listed there. Find it, and then type cd <short user name>/Desktop. Don't include the angle brackets.
Now you can use the commands mentioned above to move those files.
mkdir i_promise_to_read_carefully_next_time
mv *.jpg i_promise_to_read_carefully_next_time/
When you are finished, reboot the machine with this command:
shutdown -r now