"What can you do in cases of accidental file deletion or card failure?
Although flash memory cards are, in general, sturdy and reliable, there are times when it becomes difficult for digital camera owners to retrieve images from their camera’s memory card because the card has been corrupted in some way or because they have accidentally deleted a wanted image.
Why files get lost
Most problems are caused when the card is ejected during writing or the battery fails during writing. Other times the people accidentally delete or reformat their card. Although in some cases the damage caused by interrupting the writing process is temporary and the card can be restored to normal operability by reformatting it, permanent damage may result, making image files non-recoverable."