It highly depends on the IT prowess of the person to whom you sold it. If they are able to dig into the phone, they can get your pictures. Avast, the AV company, recently stated they were able to get pictures off of hundreds of "wiped" phones, rooted or otherwise. Your data will never be truly gone unless you microwave the phone or something. But the odds of the person having the knowledge and software needed to get your pictures is pretty slim.