A company in the Czech Republic has bought android phones off Ebay and extracted 10's of thousand of images and personal data from the phones using easily available standard forensic tools.
Although most people are aware that a factory reset usually wipes data, it seems that some of the older smart phones only erase the indexing, not that actual images/data itself.
Experts have warned the only way to be safe that your data has been wiped is to destroy the phone.
I have a sledge hammer for hire if anyone needs it 
