not the case.
data can still be recovered if overwritten. it's expensive, but it can be done. the only sure way is physical destruction.
Data is stored as a series of 0s & 1s. If the sequence is changed, as I suggested, by copying in photographs to overwrite the sequence, I am at a loss as to understand how the data may be recovered.
However, in most non domestic environments, data is backed up multiple times.
The first time this came to light in an obvious way was with Cl. Oliver North, Ronnie Reagan & the Iran/Contra affalr. Ollie deleted all the files from his computers and then told porkes to the enquiry. He did not realise all the files had been backed up 6 times, and he was seriously caught out.
I accept that data which has been deleted but not overwritten may be easily recovered. I have done it many times myself, but I would suggest that the commonly held belief that it can be recovered after overwriting is an exaggeration.
As someone who has bought dozens of computers from Ebay, usually wth hard disks not even wiped, I have never, over the years, found anything on them worth looking at. Mostly out of focus photos, and totally irrelevant spreadsheets.
Unless one is into pornographic photos, it is an irrelevance, and anyway, I don't have a pornograph to view them on if I buy such a computer!
Myke