For future reference, you could have just let it copy everything to the wrong place and used Cmd-Z to undo (as long as you didn't do anything else to stand i the event loop).
But yes, you can fix this pretty easily. Do you have another admin account or root account that you can log into? If not, that's OK too, we can boot into Single User Mode and move the files that way. I don't know your level of UNIX knowledge.. You need to know your "shortusername".
Single User Mode way:
Restart holding down Cmd-S
At the prompt, type:
mount -uw /
Press Return, then at the prompt type:
mkdir /Users/shortusername/Desktop/oops
Press Return (note, all instances of "shortname" should be replaced by your account's shortname), then at the prompt type:
cd /Users/shortusername/Desktop
Press Return, then at the prompt type:
mv *.jpg ./oops
Press Return (note, we use *.jpg assuming all the files were JPEGs, and note, that is "mv*.jpg./oops"), and then at the prompt type:
reboot
Press Return.
Now login as normal and all your waylaid pictures should be in the folder called "oops" that is on your Desktop.