How to remove your ImageShack account
From the FAQ:
It is not necessary to delete your account once you feel that you no longer need it. Simply stop using it. Otherwise send us an email and we will remove it.
Direct removal link: http://stream.imageshack.us/content.php?page=email&q=customer
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for ImageShack using a third-party login such as Facebook or Twitter, you probably want to revoke all access from ImageShack. Click here to find out how.