If they're gone from the external harddrive then it sounds like he wasn't copying the photos, he was moving them.
I don't understand the stuff you say about 'temporary memory'. If you're just copying/moving files /tmp and /var/tmp shouldn't come in to it.
The good news is that deleting files doesn't remove them from the disk, it just removes the references that say where the file is on the disk and effectively marks that part of the disk as being empty so it can be re-used.
First thing you need to do is to do as little as possible with the laptop. The more thing you do the more the chances of the parts of the harddisk where the files are being over written.
Some stuff here might be useful.
I used recently used http://www.sleuthkit.org/autopsy/desc.php
to recover a bunch of files from a dodgy disk. (Edit: Actually I might have used ddrescure. I can't remember for sure. Edit #2. It was Photorec I used. Seeing it mentioned in John VV's post reminded me and I found the remnants of using it on my disk. It worked very well. The files cam back without the original names but that's inevitable.)
What filesystem is the external harddrive formatted with?