You may be able to recover the files if:
• You mistakenly delete files from a memory card.
• You inadvertently reformat a memory card.
• The card, or some of the files on the card, become corrupted.
Recovery is often successful because usually only the card's FAT (File Allocation Table) has been deleted or corrupted.
The FAT is like the table of contents of the card.
When a file is deleted or corrupted, usually only the entry of the file in the FAT is deleted or corrupted.
The data probably remains, intact, ready to be read by recovery software.
Do the following:
1) Don't use the card.
You don't want to write over the files that are already on the memory card.
2) Go to the website of the card manufacturer for file recovery software.
For example, Lexar has Image Rescue.
3) Try the recovery software below if the card manufacturer doesn't provide any software.
File Juicer Great comments on the website
IsoBuster 1.8 CD and DVD data recovery