is it possible that pictures and videos cannot be restored?

[AC Question]

I sold my smartphone to someone and I had personal pictures and videos of family etc.. I deleted everything as well as factory restored the phone.. I'd like to know if there is any way anyone can access these photos still?

 

[belodion]

Yes, though it would not be easy.

Edit: I'm sorry, I missed your title question. Encryption of personal data before resetting is one way of rendering the data irrecoverable, and another is to overwrite your data with junk files.

 

[Rukbat]

All anyone needs is an app like Disk Digger. A few of the pictures might be damaged, but deleting files or resetting the phone just marks the pictures as deleted so that don't show, it doesn't actually delete anything. (The best way to make sure that nothing can be recovered is to reflash the ROM.)