You should use a file manager (Windows Explorer, if you have nothing else) to look inside the folders on the flash drive, with the option to view them in "list" form, to see the dates and sizes of the files. If the filesizes are zero, then the pictures have been corrupted -- and you will not be able to recover them easily.
I personally, have found flash drives to be extremely unreliable. The data recovery utilities that work well on hard drives (e.g., Recuva, RecoverMyFiles, GetDataBack) I've found to be all but useless on flash drives.
But, you can at least try one or more of these to see if they find any of the files.