Is there a law for taking your copy of a professional photo and getting it blown up?

You own the picture...you don't own the copyright to the picture. So you cannot get a copy of it made unless you are granted permission from the company who owns the copyright. Sometimes they will allow you to do it though...you could ask them. I know several photographers who give permission for a small fee.

Don't do it! You can't teach a non-photographer to have a photographer's "eye." That is something that must be trained over time, and also some innate talent as well. You can scrimp on virtually everything else, but once your wedding day is over, those moments can never be recaptured. Go with a college student who is a photography major (or at least who has had several classes). Your first instinct that you would blame the family member is 100% right on. It wouldn't be fair to the family member either if they screwed it up. After all, they are not a professional.

Yes there is a law, it has to do with copyright or work done by someone else. Even though you paid for the picture the person behind the counter has no way of knowing that and so the companies (Walgreen, CVS, Wal-Mart etc) just made it a policy not to copy professional work so they won't get sued.

Making copies of someone else's work is copywrite infringement. Yes. It's against the law.

That is copyright laws. They (the company that took your pic) have the copyright on that pic (which means they own it) and it is against the law for you to copy it.

Yes, unfortunately, even it is YOUR picture, YOU PAID for it, but still some photographer or photo company has the copy rights.Is it screwed or what, they have the right to do whatever with your picture but you can`t get YOUR OWN picture enlarged. Bless our Politician for selling our right to highest paying companies through lobbyists.

Copyright law forbids it.