"Unless somebody consciously takes it down, it will stay there pretty much permanently as long as servers are in business and we have electricity."
Dr Seel said young people were often told about the more immediate dangers of putting inappropriate content online, but there were longer-lasting effects - including how descendants would view their great-great-grandfather or mother.
"I did a paper while in college about my grandmother's life. So I interviewed her and discovered all kinds of facts that I wasn't aware of.
"Whereas young people born today, their grandchildren will be able to have access to a huge amount of information, some of which you may not want them to know."
Others would also be interested in trawling through past generations' online content.
"People joke about tweets being about trivial things, but tweeting is often about daily life ... for a sociologist or historian or anthropologist it's an incredible goldmine."
Dr Seel, who was a photojournalist and television producer and director for 10 years, teaches his students at Colorado State University how to make the internet partly "forget".
While embarrassing content often cannot be entirely removed, it can be pushed down the list of search results by newer content - fresh social content and websites linked to a person's name.
"So when people search you they won't see the goofy photos of you when you were 16 acting crazy."
Dr Pete Seel's lecture is today at 1pm in the Sir Neil Waters Lecture Theatre 100 at Massey University's Albany campus, and is open to the public.
Digital immortality
* Online posts are likely to outlive us and be accessed by descendants and historians.
* People can obscure negative material by uploading new content which will be listed first in search results.
* Companies have different policies on what happens to someone's content when they die. Instructions in a will can ensure it is not deleted and is managed correctly.
