I noticed it in, for example, the profiles of some Stack Exchange users. So I wonder: did they want to protect themselves from spamming bots this way, or ...?
Does it have to do with security? Because I guess that the bots can easily convert something like "name at email dot com" to "name@email.com"...
...or read simple images?
It's not to be the perfect security, just make spamming harder.
Spammers will have to scrap lots and lots of pages to create a database of email addresses. It's cheaper to get the text, search for a pattern like name@email.com and add to the database than to search for name at server.com, or name at server dot com, or name at server . com, and other variations, parse all, validate all and add to the database.
So the point is to not be the lower hanging fruit. You could use a javascript that needs to solve a captcha, an equation, then asks for clicking on a happy cat to show the email, but if a spammer really wants your email, he will create a bot (or use Amazon Mechanical Turk) to "solve" your riddles.
