Why do some phones still have their data even after a factory reset?

Question

This actually happened to me,

I had this old phone that had a pattern lock. obviously, I didn’t know what was the correct pattern.

so I did a factory reset. When the phone booted I saw some pictures despite there was no SD card

or anything like that. Why did the files not get erased?? especially on older devices (2010-2013)

In: Technology

Answer 1

It probably depends on what the factory reset does.

The common things to reset are things like installed programs, settings, and OS state. If the factory reset only cares about those things, then files in the photos folder can easily be ignored. If the entire file system is rebuilt, only then would your photos be at risk of getting lost.