There is no official way to tell if someone has blocked you; however, there are third party applications that can tell you when someone has unfollowed you (which happens automatically when you are blocked), such as Unfollowgram.
UPDATE 06/11/2012: This is now possible “natively” by going to instagram.com/profile_name. Source.
UPDATE 17/04/2020: But clicking any picture opens a login popup instead of details
Yes, if you know your friend’s Instagram username, you can use Webstagram. Search for his/her username and see his/her photo stream. (E.g.: Ariana Grande’s photos.) However, note that if the respective user’s profile is set to private, you can’t see the photos. Source.
Instagram doesn't place any limit on the number of accounts you can create, as long as you provide a different email address for each one. The Instagram mobile application supports signing in with only one account at a time, although third-party programs enable you to manage multiple accounts from a single interface.
Best Answer
There is no official way to tell if someone has blocked you; however, there are third party applications that can tell you when someone has unfollowed you (which happens automatically when you are blocked), such as Unfollowgram.