Well it is going to depend on how they got off the card. If it was due to formatting on either a computer or on the device, then I see no way to get them back. However if it was due to accidental deletion only, you 'may' be able to recover them. Maybe.
There are a few apps/programs out there that "may" be able to help you recover the data. I keep saying 'may' be able to as there is no guarantee in this. Once things are deleted, well they are meant to be gone. That said....
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and Tenorshare. They are all data recovery apps/programs. There are many others out there, so check around and see which you would rather try.
One important note though, most of...