In Windows, you may want to first try to set all the files as visible.
In Windows 7 / Vista:
Go to start, in the search box type
cmd and right click on the result and choose "Open as Administrator" to open an Elevated Command Prompt.
In Windows 8:
+ R to open the "Power Users Tasks Menu" and select "Command Prompt(Admin)".
From there switch to your thumb drive
e: or whatever it is and then run
ATTRIB -S -H *.* /S /D This will remove "hidden and system" flags from the files. Try and see if you can see them now.
If not, then they got corrupted by a bad removal. I had a bad thumb drive that wouldn't eject right and I had a program that I would have to run all the time to recover the files. Of course I can't find it now, but recuva is good and will probably do the same thing better.
If that fails too,
chkdsk /r on it as a last resort. Close all open windows looking at the thumb drive, other than the
cmd window. chkdsk may still ask "Do you want to force a dismount?" If you are sure you're on the thumb drive say "y". It will scan the drive and look for errors. If it finds your files were damaged, it will grab them and put them back on the drive, but possibly with different filenames.
Also--- don't put anything else on the drive while you are trying to recover your data.
Edit: Another thing you should consider is that you dropped the photos folder inside one of the other ones, maybe the videos folder.
to check, pull up
cmd switch to the thumb drive
e: (or whatever) and run
dir /S /A /p -- this way you can scroll through all of the legitimate files on the disk. You can also compare the size of the video folder to the 15.7 GB you mentioned above. Keep in mind that dir's output is in bytes, and 15.7 GB is something like 16,857,700,000 Bytes.