[Maestro]

The reason you can recover deleted files from a HDD is due the fact that when a file is deleted, the actual file is not really deleted, just the entry in the file index is deleted this tell the OS where to find the file on the actual platter of the drive. Only after some time when the drives runs it clean up routines and relocate the space where the files was stored then tells the system it is now available to write new data to this locate does the file disappears. However, when writing to this spot there is residual magnetic information store at this location which can be use to reconstruct the original data which was stored there. This is why software which wipes a drive will right alternating 1's and 0's to all the storage locations on the drive to disrupt and residual magnetic fields from data which has been stored there fore long time. Trying to get to this residual data requires going back the HDD manufactures they have the tools to look at this.

Flash memory operate in similar ways since it used almost the same data and file management systems as a HDD. A deleted file is not really deleted, it most likely is still there, only index information was removed pointing to the starting and ending point of the file. The other issue Flash has especial on devices which lots of information is stored to the device over time. Flash does what is know as wear leveling, storage cells wear out if written and erase too much, so the data management system will move data around to ensure all cells are used the same amount of time. Even if new data is writing to the device at later time in a new location as is usually done it would be rewriting to an deleted file located via the wear level algorithm.

If the file was deleted, and no new data written since it was deleted means the data is still there, the file structure index needs to be reconstructed to find the original file locate and type, so the data can be manually read from the storage location and reconstructed.

This take a profession most times to do correctly, fixing a corrupt index can be done with third party software as well as the ability to recover a delete file as long as no new data was written to the storage device after the file was deleted. I have done this on HDD many time but never tried in on Flash since more of software is made for HDD not a solid state devices.