The concept of file signatures recovery
If the data loss was caused due to a total file system failure, even the best file recovery programs can only recover the files by signature.
Signatures recognition is possible to call Last Chance data recovery.
These programs scan the whole disk's surface, using algorithms to determine the beginning of the file (specific signature), its size and file extension without relying on data
that used to be contained in the file system. This works for only un-fragmented files (stored on the disk as a continuous set of file data clusters) which means that
large files have less chances to be recovered, however this approach works fine in most cases for the Photos, Documents, Music, eBooks, Archives...
Signatures Specifications & Recovery Examples:
Photos & Images Formats
Music & Audio Files
Video & Animation Files
Microsoft Office Files & Documents
Electronic Books Files
Camera Raw Image Files
Formatted Text Files